Fix SsaForecast bug (#5023)

* fix SsaForecast

* refind comments

* remove static fields to local variable

Author: frank-dong-ms-zz

src/Microsoft.ML.TimeSeries/PolynomialUtils.cs

@@ -145,7 +145,6 @@ public FactorMultiplicity(int multiplicity = 1)
         private sealed class PolynomialFactor
         {
             public List<decimal> Coefficients;
-            public static decimal[] Destination;
 
             private decimal _key;
             public decimal Key { get { return _key; } }
@@ -175,20 +174,21 @@ internal PolynomialFactor(decimal key)
                 _key = key;
             }
 
-            public void Multiply(PolynomialFactor factor)
+            public void Multiply(PolynomialFactor factor, decimal[] destination)
             {
                 var len = Coefficients.Count;
                 Coefficients.AddRange(factor.Coefficients);
 
-                PolynomialMultiplication(0, len, len, factor.Coefficients.Count, 0, 1, 1);
+                PolynomialMultiplication(destination, 0, len, len, factor.Coefficients.Count, 0, 1, 1);
 
                 for (var i = 0; i < Coefficients.Count; ++i)
-                    Coefficients[i] = Destination[i];
+                    Coefficients[i] = destination[i];
 
                 SetKey();
             }
 
-            private void PolynomialMultiplication(int uIndex, int uLen, int vIndex, int vLen, int dstIndex, decimal uCoeff, decimal vCoeff)
+            private void PolynomialMultiplication(decimal[] destination, int uIndex, int uLen, int vIndex,
+                int vLen, int dstIndex, decimal uCoeff, decimal vCoeff)
             {
                 Contracts.Assert(uIndex >= 0);
                 Contracts.Assert(uLen >= 1);
@@ -198,18 +198,19 @@ private void PolynomialMultiplication(int uIndex, int uLen, int vIndex, int vLen
                 Contracts.Assert(vIndex + vLen <= Utils.Size(Coefficients));
                 Contracts.Assert(uIndex + uLen <= vIndex || vIndex + vLen <= uIndex); // makes sure the input ranges are non-overlapping.
                 Contracts.Assert(dstIndex >= 0);
-                Contracts.Assert(dstIndex + uLen + vLen <= Utils.Size(Destination));
+                Contracts.Assert(dstIndex + uLen + vLen <= Utils.Size(destination));
 
                 if (uLen == 1 && vLen == 1)
                 {
-                    Destination[dstIndex] = Coefficients[uIndex] * Coefficients[vIndex];
-                    Destination[dstIndex + 1] = Coefficients[uIndex] + Coefficients[vIndex];
+                    destination[dstIndex] = Coefficients[uIndex] * Coefficients[vIndex];
+                    destination[dstIndex + 1] = Coefficients[uIndex] + Coefficients[vIndex];
                 }
                 else
-                    NaivePolynomialMultiplication(uIndex, uLen, vIndex, vLen, dstIndex, uCoeff, vCoeff);
+                    NaivePolynomialMultiplication(destination, uIndex, uLen, vIndex, vLen, dstIndex, uCoeff, vCoeff);
             }
 
-            private void NaivePolynomialMultiplication(int uIndex, int uLen, int vIndex, int vLen, int dstIndex, decimal uCoeff, decimal vCoeff)
+            private void NaivePolynomialMultiplication(decimal[] destination, int uIndex, int uLen, int vIndex,
+                int vLen, int dstIndex, decimal uCoeff, decimal vCoeff)
             {
                 int i;
                 int j;
@@ -246,7 +247,7 @@ private void NaivePolynomialMultiplication(int uIndex, int uLen, int vIndex, int
                     for (j = 0; j < a; ++j)
                         temp += (Coefficients[b - j + uIndex] * Coefficients[c + j + vIndex]);
 
-                    Destination[i + dstIndex] = temp;
+                    destination[i + dstIndex] = temp;
                 }
             }
         }
@@ -285,6 +286,7 @@ public static bool FindPolynomialCoefficients(Complex[] roots, ref Double[] coef
             int destinationOffset = 0;
 
             var factors = new List<PolynomialFactor>();
+            decimal[] destination = new decimal[n];
 
             for (i = 0; i < n; ++i)
             {
@@ -336,9 +338,6 @@ public static bool FindPolynomialCoefficients(Complex[] roots, ref Double[] coef
 
             if (destinationOffset < n - 1)
             {
-                if (Utils.Size(PolynomialFactor.Destination) < n)
-                    PolynomialFactor.Destination = new decimal[n];
-
                 while (factors.Count > 1)
                 {
                     var k1 = Math.Abs(factors.ElementAt(0).Key);
@@ -364,7 +363,7 @@ public static bool FindPolynomialCoefficients(Complex[] roots, ref Double[] coef
                     var f2 = factors.ElementAt(ind);
                     factors.RemoveAt(ind);
 
-                    f1.Multiply(f2);
+                    f1.Multiply(f2, destination);
 
                     ind = factors.BinarySearch(f1, comparer);
                     if (ind >= 0)

test/Microsoft.ML.TimeSeries.Tests/TimeSeriesDirectApi.cs

@@ -328,8 +328,6 @@ public void ChangePointDetectionWithSeasonalityPredictionEngine()
         }
 
         [LessThanNetCore30OrNotNetCoreFact("netcoreapp3.1 output differs from Baseline")]
-        //Skipping test temporarily. This test will be re-enabled once the cause of failures has been determined
-        [Trait("Category", "SkipInCI")]
         public void SsaForecast()
         {
             var env = new MLContext(1);