diff --git a/README.adoc b/README.adoc
index dd4c454..3c0cce2 100644
--- a/README.adoc
+++ b/README.adoc
@@ -33,11 +33,9 @@ regarding the estimated model with respect to a set of given input values for th
 `value`:: The predicted value for the response variable computed using the estimated linear hypothesis
           function ``h(x)`` with `x` given by `C` input values for the explanatory variables
           `x = [x~1~, x~2~,...,x~C~]`.
-`coefficients`:: Estimated slope coefficients
-  image:http://latex.codecogs.com/gif.latex?\theta_1,%20\theta_2,%20\theta_3,.%20.%20.,%20\theta_C%20[]
+`coefficients`:: Estimated coefficients
+  image:http://latex.codecogs.com/gif.latex?\theta_0,%20\theta_1,%20\theta_2,%20\theta_3,.%20.%20.,%20\theta_C%20[]
     of the linear linear hypothesis function ``h(x)``.
-`intercept`:: Estimated intercept coefficient image:http://latex.codecogs.com/gif.latex?\theta_0%20[]
-                 of the linear hypothesis function ``h(x)``.
 
 Assuming the data consists of documents representing sold house prices with features
  like number of bedrooms, bathrooms and size etc. we can let predict or validate
@@ -80,11 +78,11 @@ And the following may be the response with the estimated price of around $ 581,4
         "my_house_price": {
             "value": 581458.3087492324,
             "coefficients": [
+                227990.63952712028,
                 248.92285661317254,
                 -68297.7720278421,
                 64406.52205356777
-            ],
-            "intercept": 227990.63952712028
+            ]
         }
     }
 }
@@ -99,11 +97,9 @@ The `linreg_stats` aggregation computes statistics for the estimated linear regr
 `rss`:: Residual sum of squares as a measure of the discrepancy between the data and the estimated model.
         The lower the `rss` number, the smaller the error of the prediction, and the better the model.
 `mse`:: Mean squared error or rather `rss` divided by the number of documents consumed for model estimation.
-`coefficients`:: Slope coefficients
-  image:http://latex.codecogs.com/gif.latex?\theta_1,%20\theta_2,%20\theta_3,.%20.%20.,%20\theta_C%20[]
+`coefficients`:: Estimated coefficients
+  image:http://latex.codecogs.com/gif.latex?\theta_0,%20\theta_1,%20\theta_2,%20\theta_3,.%20.%20.,%20\theta_C%20[]
     of the linear linear hypothesis function ``h(x)``.
-`intercept`:: Intercept coefficient image:http://latex.codecogs.com/gif.latex?\theta_0%20[]
-                 of the linear hypothesis function ``h(x)``.
 
 Assuming the data consists of documents representing house prices we can compute statistics for
 the estimated best fitting linear hypothesis function which predicts house prices based on number of
@@ -135,11 +131,11 @@ and the last for the response variable. The above request returns the following
             "rss": 49523788338938.734,
             "mse": 63410740510.80504,
             "coefficients": [
+                47553.18737564783,
                 -100544.0725894584,
                 45981.15827544966,
                 309.6013051477475
-            ],
-            "intercept": 47553.18737564783
+            ]
         }
     }
 }
@@ -180,7 +176,8 @@ Do not forget to restart the node after installing.
 [frame="all"]
 |===
 | Plugin version | Elasticsearch version | Release date
-| https://github.com/scaleborn/elasticsearch-linear-regression/releases/download/5.3.0.1/elasticsearch-linear-regression-5.3.0.1.zip[5.3.0.1]        | 5.3.0 | Jun  1, 2017
+| https://github.com/scaleborn/elasticsearch-linear-regression/releases/download/5.3.0.1/elasticsearch-linear-regression-5.3.0.2.zip[5.3.0.2]        | 5.3.0 | Jul  16, 2017
+| https://github.com/scaleborn/elasticsearch-linear-regression/releases/download/5.3.0.1/elasticsearch-linear-regression-5.3.0.1.zip[5.3.0.1]        | 5.3.0 | Jun  30, 2017
 |===
 
 ## Examples
@@ -198,7 +195,7 @@ https://github.com/scaleborn/elasticsearch-linear-regression/tree/master/example
 ./bin/logstash -f house-prices-import.conf
 ....
 
-The indexed data will have this form:
+The indexed documents will have this form:
 [source,js]
 --------------------------------------------------
 {
@@ -250,16 +247,97 @@ $ 650,000 to pay for the desired house in "Morro Bay".
         "dream_house_price": {
             "value": 649918.0709489314,
             "coefficients": [
+                228318.6161854365,
                 249.02340193904183,
                 -68314.4830871133,
                 64248.05007337558
-            ],
-            "intercept": 228318.6161854365
+            ]
         }
     }
 }
 --------------------------------------------------
 
+By using sub aggregations we are able to find out the estimated prices per location:
+[source,js]
+--------------------------------------------------
+/houses/_search?size=0
+{
+    "aggs": {
+        "locations": {
+            "terms": {
+                "field": "location.keyword",
+                "size": 15
+            },
+            "aggs": {
+                "dream_house_price": {
+                    "linreg_predict": {
+                        "fields": ["size", "bedrooms", "bathrooms", "price"],
+                        "inputs": [2000, 3, 2]
+                    }
+                }
+            }
+        }
+    }
+}
+--------------------------------------------------
+
+The response uncovers that "Arroyo Grande" would be
+the most expensive region for our dream house:
+
+[source,js]
+--------------------------------------------------
+{
+    "aggregations": {
+        "locations": {
+            "buckets": [
+                {
+                    "key": "Santa Maria-Orcutt",
+                    "doc_count": 265,
+                    "dream_house_price": {
+                        "value": 256251.9105297585,
+                        "coefficients": [
+                            26437.192829649313,
+                            81.19071633227178,
+                            6825.9128627023265,
+                            23477.773223729317
+                        ]
+                    }
+                },
+                {
+                    "key": "Paso Robles",
+                    "doc_count": 85,
+                    "dream_house_price": {
+                        "value": 365620.0386191703,
+                        "coefficients": [
+                            42958.257094706176,
+                            151.7000907380368,
+                            6486.477078139843,
+                            -98.91559301451247
+                        ]
+                    }
+                },
+                ...
+                {
+                    "key": " Arroyo Grande",
+                    "doc_count": 12,
+                    "dream_house_price": {
+                        "value": 1140196.791331573,
+                        "coefficients": [
+                            728566.7474390095,
+                            1956.6474540196602,
+                            -706891.620925945,
+                            -690495.0006844609
+                        ]
+                    }
+                }
+                ...
+            ]
+        }
+    }
+}
+--------------------------------------------------
+
+
 ## License
 Copyright 2017 Scaleborn UG (haftungsbeschränkt).
 
diff --git a/gradle.properties b/gradle.properties
index a1b3326..f5b1455 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -4,4 +4,4 @@ wagon-ssh-external.version=2.10
 commons-math3.version=3.6.1
 group=org.scaleborn.elasticsearch.plugin
 name=elasticsearch-linear-regression
-version=5.3.0.1
+version=5.3.0.2
diff --git a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/predict/InternalPrediction.java b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/predict/InternalPrediction.java
index a1eb17d..36a2fa6 100644
--- a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/predict/InternalPrediction.java
+++ b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/predict/InternalPrediction.java
@@ -25,7 +25,7 @@
 import org.elasticsearch.common.logging.Loggers;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.scaleborn.elasticsearch.linreg.aggregation.support.BaseInternalAggregation;
-import org.scaleborn.linereg.evaluation.SlopeCoefficients;
+import org.scaleborn.linereg.estimation.SlopeCoefficients;
 
 /**
  * Created by mbok on 11.04.17.
diff --git a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/predict/PredictionResults.java b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/predict/PredictionResults.java
index 8444358..80fd34d 100644
--- a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/predict/PredictionResults.java
+++ b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/predict/PredictionResults.java
@@ -22,7 +22,7 @@
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.search.aggregations.InternalAggregation.CommonFields;
 import org.scaleborn.elasticsearch.linreg.aggregation.support.ModelResults;
-import org.scaleborn.linereg.evaluation.SlopeCoefficients;
+import org.scaleborn.linereg.estimation.SlopeCoefficients;
 
 /**
  * Created by mbok on 11.04.17.
diff --git a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/stats/InternalStats.java b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/stats/InternalStats.java
index 2279564..b8f0c98 100644
--- a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/stats/InternalStats.java
+++ b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/stats/InternalStats.java
@@ -27,7 +27,7 @@
 import org.scaleborn.linereg.calculation.statistics.Statistics;
 import org.scaleborn.linereg.calculation.statistics.StatsCalculator;
 import org.scaleborn.linereg.calculation.statistics.StatsModel;
-import org.scaleborn.linereg.evaluation.SlopeCoefficients;
+import org.scaleborn.linereg.estimation.SlopeCoefficients;
 
 /**
  * Created by mbok on 21.03.17.
diff --git a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/stats/StatsResults.java b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/stats/StatsResults.java
index 00884b6..aa3324e 100644
--- a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/stats/StatsResults.java
+++ b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/stats/StatsResults.java
@@ -23,7 +23,7 @@
 import org.scaleborn.elasticsearch.linreg.aggregation.support.ModelResults;
 import org.scaleborn.linereg.calculation.statistics.Statistics;
 import org.scaleborn.linereg.calculation.statistics.Statistics.DefaultStatistics;
-import org.scaleborn.linereg.evaluation.SlopeCoefficients;
+import org.scaleborn.linereg.estimation.SlopeCoefficients;
 
 /**
  * Created by mbok on 07.04.17.
diff --git a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/support/BaseInternalAggregation.java b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/support/BaseInternalAggregation.java
index f3f5922..e52eb19 100644
--- a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/support/BaseInternalAggregation.java
+++ b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/support/BaseInternalAggregation.java
@@ -30,11 +30,12 @@
 import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.scaleborn.linereg.calculation.intercept.InterceptCalculator;
-import org.scaleborn.linereg.evaluation.DerivationEquation;
-import org.scaleborn.linereg.evaluation.DerivationEquationBuilder;
-import org.scaleborn.linereg.evaluation.DerivationEquationSolver;
-import org.scaleborn.linereg.evaluation.SlopeCoefficients;
-import org.scaleborn.linereg.evaluation.commons.CommonsMathSolver;
+import org.scaleborn.linereg.estimation.DerivationEquation;
+import org.scaleborn.linereg.estimation.DerivationEquationBuilder;
+import org.scaleborn.linereg.estimation.DerivationEquationSolver;
+import org.scaleborn.linereg.estimation.DerivationEquationSolver.EstimationException;
+import org.scaleborn.linereg.estimation.SlopeCoefficients;
+import org.scaleborn.linereg.estimation.commons.CommonsMathSolver;
 
 /**
  * Created by mbok on 07.04.17.
@@ -142,9 +143,7 @@ public InternalAggregation doReduce(final List<InternalAggregation> aggregations
 
     // return empty result if all samples are null
     if (aggs.isEmpty()) {
-      return buildInternalAggregation(this.name, this.featuresCount, null, null,
-          pipelineAggregators(),
-          getMetaData());
+      return buildEmptyInternalAggregation();
     }
 
     final S composedSampling = buildSampling(this.featuresCount);
@@ -154,7 +153,21 @@ public InternalAggregation doReduce(final List<InternalAggregation> aggregations
       composedSampling.merge((S) ((BaseInternalAggregation) aggs.get(i)).sampling);
     }
 
-    final M evaluatedResults = evaluateResults(composedSampling);
+    if (composedSampling.getCount() <= composedSampling.getFeaturesCount()) {
+      LOGGER.debug(
+          "Insufficient amount of training data for model estimation, at least {} are required, given {}",
+          composedSampling.getFeaturesCount() + 1, composedSampling.getCount());
+      return buildEmptyInternalAggregation();
+    }
+
+    M evaluatedResults = null;
+    try {
+      evaluatedResults = evaluateResults(composedSampling);
+    } catch (final EstimationException e) {
+      LOGGER.debug(
+          "Failed to estimate model", e);
+      return buildEmptyInternalAggregation();
+    }
 
     LOGGER.debug("Evaluated results: {}", evaluatedResults);
     return buildInternalAggregation(this.name, this.featuresCount, composedSampling,
@@ -162,6 +175,12 @@ public InternalAggregation doReduce(final List<InternalAggregation> aggregations
         pipelineAggregators(), getMetaData());
   }
 
+  private InternalAggregation buildEmptyInternalAggregation() {
+    return buildInternalAggregation(this.name, this.featuresCount, null, null,
+        pipelineAggregators(),
+        getMetaData());
+  }
+
   protected abstract A buildInternalAggregation(final String name, final int featuresCount,
       final S linRegSampling,
       final M results,
@@ -171,12 +190,12 @@ protected abstract M buildResults(S composedSampling, SlopeCoefficients slopeCoe
       double intercept);
 
 
-  private M evaluateResults(final S composedSampling) {
-    // Linear regression evaluation
+  private M evaluateResults(final S composedSampling) throws EstimationException {
+    // Linear regression estimation
     final DerivationEquation derivationEquation = derivationEquationBuilder
         .buildDerivationEquation(composedSampling);
     final SlopeCoefficients slopeCoefficients = derivationEquationSolver
-        .solveCoefficients(derivationEquation);
+        .estimateCoefficients(derivationEquation);
     final M buildResults = buildResults(composedSampling, slopeCoefficients,
         interceptCalculator.calculate(slopeCoefficients, composedSampling, composedSampling));
     return buildResults;
diff --git a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/support/BaseSampling.java b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/support/BaseSampling.java
index 0774ca9..8c56d6c 100644
--- a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/support/BaseSampling.java
+++ b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/support/BaseSampling.java
@@ -17,7 +17,7 @@
 package org.scaleborn.elasticsearch.linreg.aggregation.support;
 
 import java.io.IOException;
-import org.scaleborn.linereg.evaluation.SlopeCoefficientsSampling.SlopeCoefficientsSamplingProxy;
+import org.scaleborn.linereg.estimation.SlopeCoefficientsSampling.SlopeCoefficientsSamplingProxy;
 import org.scaleborn.linereg.sampling.Sampling.InterceptSampling;
 import org.scaleborn.linereg.sampling.io.StateInputStream;
 import org.scaleborn.linereg.sampling.io.StateOutputStream;
diff --git a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/support/ModelResults.java b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/support/ModelResults.java
index 2d575fb..4de3156 100644
--- a/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/support/ModelResults.java
+++ b/src/main/java/org/scaleborn/elasticsearch/linreg/aggregation/support/ModelResults.java
@@ -17,69 +17,52 @@
 package org.scaleborn.elasticsearch.linreg.aggregation.support;
 
 import java.io.IOException;
+import java.util.Arrays;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
-import org.scaleborn.linereg.evaluation.SlopeCoefficients;
-import org.scaleborn.linereg.evaluation.SlopeCoefficients.DefaultSlopeCoefficients;
+import org.scaleborn.linereg.estimation.SlopeCoefficients;
 
 /**
  * Created by mbok on 07.04.17.
  */
 public class ModelResults implements Writeable, ToXContent {
 
-  private SlopeCoefficients slopeCoefficients;
-
-  private double intercept;
+  private final double[] coefficients;
 
   public ModelResults(final SlopeCoefficients slopeCoefficients, final double intercept) {
-    this.slopeCoefficients = slopeCoefficients;
-    this.intercept = intercept;
+    final int slopeLen = slopeCoefficients.getCoefficients().length;
+    this.coefficients = new double[slopeLen + 1];
+    System.arraycopy(slopeCoefficients.getCoefficients(), 0, this.coefficients, 1, slopeLen);
+    this.coefficients[0] = intercept;
   }
 
   public ModelResults(final StreamInput in) throws IOException {
-    this.slopeCoefficients = new DefaultSlopeCoefficients(in.readDoubleArray());
-    this.intercept = in.readDouble();
+    this.coefficients = in.readDoubleArray();
   }
 
   @Override
   public void writeTo(final StreamOutput out) throws IOException {
-    out.writeDoubleArray(this.slopeCoefficients.getCoefficients());
-    out.writeDouble(this.intercept);
-  }
-
-  public SlopeCoefficients getSlopeCoefficients() {
-    return this.slopeCoefficients;
-  }
-
-  public void setSlopeCoefficients(final SlopeCoefficients slopeCoefficients) {
-    this.slopeCoefficients = slopeCoefficients;
-  }
-
-  public double getIntercept() {
-    return this.intercept;
+    out.writeDoubleArray(this.coefficients);
   }
 
-  public void setIntercept(final double intercept) {
-    this.intercept = intercept;
+  public double[] getCoefficients() {
+    return this.coefficients;
   }
 
-
   @Override
   public String toString() {
     return "ModelResults{" +
-        "slopeCoefficients=" + this.slopeCoefficients +
-        ", intercept=" + this.intercept +
+        "coefficients=" + Arrays.toString(this.coefficients) +
         '}';
   }
 
   @Override
   public XContentBuilder toXContent(final XContentBuilder builder, final Params params)
       throws IOException {
-    builder.array("coefficients", this.getSlopeCoefficients().getCoefficients());
-    builder.field("intercept", this.getIntercept());
+    builder.array("coefficients", this.coefficients);
     return builder;
   }
 
diff --git a/src/main/java/org/scaleborn/linereg/calculation/intercept/InterceptCalculator.java b/src/main/java/org/scaleborn/linereg/calculation/intercept/InterceptCalculator.java
index 7ebb1b2..a308912 100644
--- a/src/main/java/org/scaleborn/linereg/calculation/intercept/InterceptCalculator.java
+++ b/src/main/java/org/scaleborn/linereg/calculation/intercept/InterceptCalculator.java
@@ -16,7 +16,7 @@
 
 package org.scaleborn.linereg.calculation.intercept;
 
-import org.scaleborn.linereg.evaluation.SlopeCoefficients;
+import org.scaleborn.linereg.estimation.SlopeCoefficients;
 import org.scaleborn.linereg.sampling.Sampling.InterceptSampling;
 import org.scaleborn.linereg.sampling.Sampling.SamplingContext;
 
diff --git a/src/main/java/org/scaleborn/linereg/calculation/statistics/StatsModel.java b/src/main/java/org/scaleborn/linereg/calculation/statistics/StatsModel.java
index 6bbc2df..d6d2b8b 100644
--- a/src/main/java/org/scaleborn/linereg/calculation/statistics/StatsModel.java
+++ b/src/main/java/org/scaleborn/linereg/calculation/statistics/StatsModel.java
@@ -16,7 +16,7 @@
 
 package org.scaleborn.linereg.calculation.statistics;
 
-import org.scaleborn.linereg.evaluation.SlopeCoefficients;
+import org.scaleborn.linereg.estimation.SlopeCoefficients;
 
 /**
  * Bean for evaluated linear model fitting best the sampled data regarding
diff --git a/src/main/java/org/scaleborn/linereg/calculation/statistics/StatsSampling.java b/src/main/java/org/scaleborn/linereg/calculation/statistics/StatsSampling.java
index 50f1c7f..96a71ac 100644
--- a/src/main/java/org/scaleborn/linereg/calculation/statistics/StatsSampling.java
+++ b/src/main/java/org/scaleborn/linereg/calculation/statistics/StatsSampling.java
@@ -17,7 +17,7 @@
 package org.scaleborn.linereg.calculation.statistics;
 
 import java.io.IOException;
-import org.scaleborn.linereg.evaluation.SlopeCoefficientsSampling;
+import org.scaleborn.linereg.estimation.SlopeCoefficientsSampling;
 import org.scaleborn.linereg.sampling.Sampling.ResponseVarianceTermSampling;
 import org.scaleborn.linereg.sampling.io.StateInputStream;
 import org.scaleborn.linereg.sampling.io.StateOutputStream;
diff --git a/src/main/java/org/scaleborn/linereg/evaluation/DerivationEquation.java b/src/main/java/org/scaleborn/linereg/estimation/DerivationEquation.java
similarity index 96%
rename from src/main/java/org/scaleborn/linereg/evaluation/DerivationEquation.java
rename to src/main/java/org/scaleborn/linereg/estimation/DerivationEquation.java
index d0c55da..f47b989 100644
--- a/src/main/java/org/scaleborn/linereg/evaluation/DerivationEquation.java
+++ b/src/main/java/org/scaleborn/linereg/estimation/DerivationEquation.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.scaleborn.linereg.evaluation;
+package org.scaleborn.linereg.estimation;
 
 /**
  * Represents the derivation equation (divided by 2) build up from the sampled data.
diff --git a/src/main/java/org/scaleborn/linereg/evaluation/DerivationEquationBuilder.java b/src/main/java/org/scaleborn/linereg/estimation/DerivationEquationBuilder.java
similarity index 91%
rename from src/main/java/org/scaleborn/linereg/evaluation/DerivationEquationBuilder.java
rename to src/main/java/org/scaleborn/linereg/estimation/DerivationEquationBuilder.java
index bacbba8..72dce35 100644
--- a/src/main/java/org/scaleborn/linereg/evaluation/DerivationEquationBuilder.java
+++ b/src/main/java/org/scaleborn/linereg/estimation/DerivationEquationBuilder.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.scaleborn.linereg.evaluation;
+package org.scaleborn.linereg.estimation;
 
 /**
  * Created by mbok on 17.03.17.
@@ -22,7 +22,7 @@
 public class DerivationEquationBuilder {
 
   public DerivationEquation buildDerivationEquation(
-      SlopeCoefficientsSampling slopeCoefficientsSampling) {
+      final SlopeCoefficientsSampling slopeCoefficientsSampling) {
 
     return new DerivationEquation() {
       @Override
diff --git a/src/main/java/org/scaleborn/linereg/evaluation/DerivationEquationSolver.java b/src/main/java/org/scaleborn/linereg/estimation/DerivationEquationSolver.java
similarity index 63%
rename from src/main/java/org/scaleborn/linereg/evaluation/DerivationEquationSolver.java
rename to src/main/java/org/scaleborn/linereg/estimation/DerivationEquationSolver.java
index 0e0de95..5f56506 100644
--- a/src/main/java/org/scaleborn/linereg/evaluation/DerivationEquationSolver.java
+++ b/src/main/java/org/scaleborn/linereg/estimation/DerivationEquationSolver.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.scaleborn.linereg.evaluation;
+package org.scaleborn.linereg.estimation;
 
 /**
  * Solves the derivation equation and returns the coefficients for the best fit prediction
@@ -24,12 +24,26 @@
 public interface DerivationEquationSolver {
 
   /**
-   * Solves the derivation equation and returns the coefficients for the best fit prediction
-   * equation.
+   * Solves the derivation equation and returns the estimated coefficients for the best fit
+   * prediction equation.
    *
    * @param eq the derivation equation to solve. The input parameter should remain unchanged for
    * further calculations.
    * @return the slope coefficients (excluding the intercept) for the best fit prediction equation
    */
-  SlopeCoefficients solveCoefficients(DerivationEquation eq);
+  SlopeCoefficients estimateCoefficients(DerivationEquation eq) throws EstimationException;
+
+  /**
+   * Thrown when estimation fails, usually due to linearly dependent data.
+   */
+  public class EstimationException extends Exception {
+
+    public EstimationException(final String message) {
+      super(message);
+    }
+
+    public EstimationException(final String message, final Throwable cause) {
+      super(message, cause);
+    }
+  }
 }
diff --git a/src/main/java/org/scaleborn/linereg/evaluation/SlopeCoefficients.java b/src/main/java/org/scaleborn/linereg/estimation/SlopeCoefficients.java
similarity index 89%
rename from src/main/java/org/scaleborn/linereg/evaluation/SlopeCoefficients.java
rename to src/main/java/org/scaleborn/linereg/estimation/SlopeCoefficients.java
index 3791e08..556632c 100644
--- a/src/main/java/org/scaleborn/linereg/evaluation/SlopeCoefficients.java
+++ b/src/main/java/org/scaleborn/linereg/estimation/SlopeCoefficients.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.scaleborn.linereg.evaluation;
+package org.scaleborn.linereg.estimation;
 
 import java.util.Arrays;
 
@@ -35,13 +35,13 @@ public DefaultSlopeCoefficients(final double[] coefficients) {
 
     @Override
     public double[] getCoefficients() {
-      return coefficients;
+      return this.coefficients;
     }
 
     @Override
     public String toString() {
       return "DefaultSlopeCoefficients{" +
-          "coefficients=" + Arrays.toString(coefficients) +
+          "coefficients=" + Arrays.toString(this.coefficients) +
           '}';
     }
   }
diff --git a/src/main/java/org/scaleborn/linereg/evaluation/SlopeCoefficientsSampling.java b/src/main/java/org/scaleborn/linereg/estimation/SlopeCoefficientsSampling.java
similarity index 99%
rename from src/main/java/org/scaleborn/linereg/evaluation/SlopeCoefficientsSampling.java
rename to src/main/java/org/scaleborn/linereg/estimation/SlopeCoefficientsSampling.java
index 48ae091..7be3947 100644
--- a/src/main/java/org/scaleborn/linereg/evaluation/SlopeCoefficientsSampling.java
+++ b/src/main/java/org/scaleborn/linereg/estimation/SlopeCoefficientsSampling.java
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.scaleborn.linereg.evaluation;
+package org.scaleborn.linereg.estimation;
 
 import java.io.IOException;
 import org.scaleborn.linereg.sampling.Sampling.CoefficientLinearTermSampling;
diff --git a/src/main/java/org/scaleborn/linereg/evaluation/commons/CommonsMathSolver.java b/src/main/java/org/scaleborn/linereg/estimation/commons/CommonsMathSolver.java
similarity index 57%
rename from src/main/java/org/scaleborn/linereg/evaluation/commons/CommonsMathSolver.java
rename to src/main/java/org/scaleborn/linereg/estimation/commons/CommonsMathSolver.java
index 2f8ccae..26fabe8 100644
--- a/src/main/java/org/scaleborn/linereg/evaluation/commons/CommonsMathSolver.java
+++ b/src/main/java/org/scaleborn/linereg/estimation/commons/CommonsMathSolver.java
@@ -14,18 +14,19 @@
  * limitations under the License.
  */
 
-package org.scaleborn.linereg.evaluation.commons;
+package org.scaleborn.linereg.estimation.commons;
 
 import org.apache.commons.math3.linear.Array2DRowRealMatrix;
 import org.apache.commons.math3.linear.ArrayRealVector;
 import org.apache.commons.math3.linear.CholeskyDecomposition;
 import org.apache.commons.math3.linear.DecompositionSolver;
+import org.apache.commons.math3.linear.NonPositiveDefiniteMatrixException;
 import org.apache.commons.math3.linear.RealMatrix;
 import org.apache.commons.math3.linear.RealVector;
-import org.scaleborn.linereg.evaluation.DerivationEquation;
-import org.scaleborn.linereg.evaluation.DerivationEquationSolver;
-import org.scaleborn.linereg.evaluation.SlopeCoefficients;
-import org.scaleborn.linereg.evaluation.SlopeCoefficients.DefaultSlopeCoefficients;
+import org.scaleborn.linereg.estimation.DerivationEquation;
+import org.scaleborn.linereg.estimation.DerivationEquationSolver;
+import org.scaleborn.linereg.estimation.SlopeCoefficients;
+import org.scaleborn.linereg.estimation.SlopeCoefficients.DefaultSlopeCoefficients;
 
 /**
  * Solves the coefficient derivation equation using math-commons library and the Cholesky
@@ -34,16 +35,17 @@
 public class CommonsMathSolver implements DerivationEquationSolver {
 
   @Override
-  public SlopeCoefficients solveCoefficients(final DerivationEquation eq) {
-    double[][] sourceTriangleMatrix = eq.getCovarianceLowerTriangularMatrix();
+  public SlopeCoefficients estimateCoefficients(final DerivationEquation eq)
+      throws EstimationException {
+    final double[][] sourceTriangleMatrix = eq.getCovarianceLowerTriangularMatrix();
     // Copy matrix and enhance it to a full matrix as expected by CholeskyDecomposition
     // FIXME: Avoid copy job to speed-up the solving process e.g. by extending the CholeskyDecomposition constructor
-    int length = sourceTriangleMatrix.length;
-    double[][] matrix = new double[length][];
+    final int length = sourceTriangleMatrix.length;
+    final double[][] matrix = new double[length][];
     for (int i = 0; i < length; i++) {
       matrix[i] = new double[length];
-      double[] s = sourceTriangleMatrix[i];
-      double[] t = matrix[i];
+      final double[] s = sourceTriangleMatrix[i];
+      final double[] t = matrix[i];
       for (int j = 0; j <= i; j++) {
         t[j] = s[j];
       }
@@ -51,11 +53,15 @@ public SlopeCoefficients solveCoefficients(final DerivationEquation eq) {
         t[j] = sourceTriangleMatrix[j][i];
       }
     }
-    RealMatrix coefficients =
+    final RealMatrix coefficients =
         new Array2DRowRealMatrix(matrix, false);
-    DecompositionSolver solver = new CholeskyDecomposition(coefficients).getSolver();
-    RealVector constants = new ArrayRealVector(eq.getConstraints(), true);
-    final RealVector solution = solver.solve(constants);
-    return new DefaultSlopeCoefficients(solution.toArray());
+    try {
+      final DecompositionSolver solver = new CholeskyDecomposition(coefficients).getSolver();
+      final RealVector constants = new ArrayRealVector(eq.getConstraints(), true);
+      final RealVector solution = solver.solve(constants);
+      return new DefaultSlopeCoefficients(solution.toArray());
+    } catch (final NonPositiveDefiniteMatrixException e) {
+      throw new EstimationException("Matrix inversion error due to data is linearly dependent", e);
+    }
   }
 }
diff --git a/src/test/java/org/scaleborn/linereg/TestModels.java b/src/test/java/org/scaleborn/linereg/TestModels.java
index 1715a54..44a3adc 100644
--- a/src/test/java/org/scaleborn/linereg/TestModels.java
+++ b/src/test/java/org/scaleborn/linereg/TestModels.java
@@ -25,10 +25,11 @@
 import org.scaleborn.linereg.calculation.statistics.StatsModel;
 import org.scaleborn.linereg.calculation.statistics.StatsSampling;
 import org.scaleborn.linereg.calculation.statistics.StatsSampling.StatsSamplingProxy;
-import org.scaleborn.linereg.evaluation.DerivationEquation;
-import org.scaleborn.linereg.evaluation.DerivationEquationBuilder;
-import org.scaleborn.linereg.evaluation.SlopeCoefficients;
-import org.scaleborn.linereg.evaluation.commons.CommonsMathSolver;
+import org.scaleborn.linereg.estimation.DerivationEquation;
+import org.scaleborn.linereg.estimation.DerivationEquationBuilder;
+import org.scaleborn.linereg.estimation.DerivationEquationSolver.EstimationException;
+import org.scaleborn.linereg.estimation.SlopeCoefficients;
+import org.scaleborn.linereg.estimation.commons.CommonsMathSolver;
 import org.scaleborn.linereg.sampling.exact.ExactModelSamplingFactory;
 import org.scaleborn.linereg.sampling.exact.ExactSamplingContext;
 
@@ -105,8 +106,8 @@ public DerivationEquation getEquation() {
       return this.equation;
     }
 
-    public StatsModel evaluateModel() {
-      final SlopeCoefficients coefficients = new CommonsMathSolver().solveCoefficients(
+    public StatsModel evaluateModel() throws EstimationException {
+      final SlopeCoefficients coefficients = new CommonsMathSolver().estimateCoefficients(
           this.equation);
       return new StatsModel(this.statsSampling, coefficients);
     }
diff --git a/src/test/java/org/scaleborn/linereg/calculation/statistics/StatsBuilderTests.java b/src/test/java/org/scaleborn/linereg/calculation/statistics/StatsBuilderTests.java
index 3b3a3e5..e56db05 100644
--- a/src/test/java/org/scaleborn/linereg/calculation/statistics/StatsBuilderTests.java
+++ b/src/test/java/org/scaleborn/linereg/calculation/statistics/StatsBuilderTests.java
@@ -20,6 +20,7 @@
 import org.junit.Test;
 import org.scaleborn.linereg.TestModels;
 import org.scaleborn.linereg.TestModels.TestModel;
+import org.scaleborn.linereg.estimation.DerivationEquationSolver.EstimationException;
 
 /**
  * Tests for {@link StatsCalculator}.
@@ -28,14 +29,14 @@
 public class StatsBuilderTests extends ESTestCase {
 
   @Test
-  public void testStats() {
+  public void testStats() throws EstimationException {
     testStatsForModel(TestModels.SIMPLE_MODEL_1);
     testStatsForModel(TestModels.MULTI_FEATURES_2_MODEL_1);
     testStatsForModel(TestModels.MULTI_FEATURES_3_MODEL_1);
     testStatsForModel(TestModels.MULTI_FEATURES_6_LONGLEY);
   }
 
-  private void testStatsForModel(final TestModel testModel) {
+  private void testStatsForModel(final TestModel testModel) throws EstimationException {
     final StatsModel linearModel = testModel.evaluateModel();
     final Statistics statistics = new StatsCalculator().calculate(linearModel);
     testModel.assertStatistics(statistics);
diff --git a/src/test/java/org/scaleborn/linereg/estimation/commons/CommonsMathSolverTests.java b/src/test/java/org/scaleborn/linereg/estimation/commons/CommonsMathSolverTests.java
new file mode 100644
index 0000000..66a7441
--- /dev/null
+++ b/src/test/java/org/scaleborn/linereg/estimation/commons/CommonsMathSolverTests.java
@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2017 Scaleborn UG, www.scaleborn.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.scaleborn.linereg.estimation.commons;
+
+import org.elasticsearch.test.ESTestCase;
+import org.junit.Test;
+import org.scaleborn.linereg.TestModels;
+import org.scaleborn.linereg.TestModels.TestModel;
+import org.scaleborn.linereg.estimation.DerivationEquation;
+import org.scaleborn.linereg.estimation.DerivationEquationSolver.EstimationException;
+
+/**
+ * Created by mbok on 18.03.17.
+ */
+public class CommonsMathSolverTests extends ESTestCase {
+
+  /**
+   * Tests coefficient estimation with one feature variable.
+   */
+  @Test
+  public void testSimpleRegression() throws EstimationException {
+    final TestModel model = TestModels.SIMPLE_MODEL_1;
+    final DerivationEquation equation = model.getEquation();
+    final double[] coefficients = new CommonsMathSolver().estimateCoefficients(equation)
+        .getCoefficients();
+    this.logger.info("Evaluated linreg coefficients: {}", coefficients);
+    model.assertCoefficients(coefficients, 0.0000001);
+  }
+
+  /**
+   * Tests coefficient estimation with two feature variables.
+   */
+  @Test
+  public void testMultipleRegressionWith2Features() throws EstimationException {
+    final TestModel testModel = TestModels.MULTI_FEATURES_2_MODEL_1;
+    final double[] coefficients = new CommonsMathSolver()
+        .estimateCoefficients(testModel.getEquation())
+        .getCoefficients();
+    this.logger.info("Evaluated linreg coefficients: {}", coefficients);
+    testModel.assertCoefficients(coefficients, 0.0000001);
+  }
+
+  /**
+   * Tests coefficient estimation with three feature variables.
+   */
+  @Test
+  public void testMultipleRegressionWith3Features() throws EstimationException {
+    final TestModel testModel = TestModels.MULTI_FEATURES_3_MODEL_1;
+    final DerivationEquation equation = testModel.getEquation();
+    final double[] coefficients = new CommonsMathSolver().estimateCoefficients(equation)
+        .getCoefficients();
+    this.logger.info("Evaluated linreg coefficients: {}", coefficients);
+    testModel.assertCoefficients(coefficients, 0.0000001);
+  }
+
+  /**
+   * Tests coefficient estimation with the reference Longley data set.
+   */
+  @Test
+  public void testMultipleRegressionWithLongleyDataSet() throws EstimationException {
+    final TestModel testModel = TestModels.MULTI_FEATURES_6_LONGLEY;
+    final DerivationEquation equation = testModel.getEquation();
+    final double[] coefficients = new CommonsMathSolver().estimateCoefficients(equation)
+        .getCoefficients();
+    this.logger.info("Evaluated linreg coefficients for longley data set: {}", coefficients);
+    testModel.assertCoefficients(coefficients, 0.0000001);
+  }
+}
diff --git a/src/test/java/org/scaleborn/linereg/evaluation/commons/CommonsMathSolverTests.java b/src/test/java/org/scaleborn/linereg/evaluation/commons/CommonsMathSolverTests.java
deleted file mode 100644
index 20706a7..0000000
--- a/src/test/java/org/scaleborn/linereg/evaluation/commons/CommonsMathSolverTests.java
+++ /dev/null
@@ -1,77 +0,0 @@
-/*
- * Copyright (c) 2017 Scaleborn UG, www.scaleborn.com
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.scaleborn.linereg.evaluation.commons;
-
-import org.elasticsearch.test.ESTestCase;
-import org.junit.Test;
-import org.scaleborn.linereg.TestModels;
-import org.scaleborn.linereg.TestModels.TestModel;
-import org.scaleborn.linereg.evaluation.DerivationEquation;
-
-/**
- * Created by mbok on 18.03.17.
- */
-public class CommonsMathSolverTests extends ESTestCase {
-
-  /**
-   * Tests coefficient evaluation with one feature variable.
-   */
-  @Test
-  public void testSimpleRegression() {
-    TestModel model = TestModels.SIMPLE_MODEL_1;
-    DerivationEquation equation = model.getEquation();
-    double[] coefficients = new CommonsMathSolver().solveCoefficients(equation).getCoefficients();
-    logger.info("Evaluated linreg coefficients: {}", coefficients);
-    model.assertCoefficients(coefficients, 0.0000001);
-  }
-
-  /**
-   * Tests coefficient evaluation with two feature variables.
-   */
-  @Test
-  public void testMultipleRegressionWith2Features() {
-    TestModel testModel = TestModels.MULTI_FEATURES_2_MODEL_1;
-    double[] coefficients = new CommonsMathSolver().solveCoefficients(testModel.getEquation())
-        .getCoefficients();
-    logger.info("Evaluated linreg coefficients: {}", coefficients);
-    testModel.assertCoefficients(coefficients, 0.0000001);
-  }
-
-  /**
-   * Tests coefficient evaluation with three feature variables.
-   */
-  @Test
-  public void testMultipleRegressionWith3Features() {
-    TestModel testModel = TestModels.MULTI_FEATURES_3_MODEL_1;
-    DerivationEquation equation = testModel.getEquation();
-    double[] coefficients = new CommonsMathSolver().solveCoefficients(equation).getCoefficients();
-    logger.info("Evaluated linreg coefficients: {}", coefficients);
-    testModel.assertCoefficients(coefficients, 0.0000001);
-  }
-
-  /**
-   * Tests coefficient evaluation with the reference Longley data set.
-   */
-  @Test
-  public void testMultipleRegressionWithLongleyDataSet() {
-    TestModel testModel = TestModels.MULTI_FEATURES_6_LONGLEY;
-    DerivationEquation equation = testModel.getEquation();
-    double[] coefficients = new CommonsMathSolver().solveCoefficients(equation).getCoefficients();
-    logger.info("Evaluated linreg coefficients for longley data set: {}", coefficients);
-    testModel.assertCoefficients(coefficients, 0.0000001);
-  }
-}