feat(det): add 2x2 and 3x3 determinants

Author: zafarali

src/abstractMatrix.js

@@ -1502,6 +1502,52 @@ function abstractMatrix(superCtor) {
         selectionView(rowIndices, columnIndices) {
             return new MatrixSelectionView(this, rowIndices, columnIndices);
         }
+
+
+        /**
+        * Calculates and returns the determinant of a matrix as a Number
+        * @example
+        *   new Matrix([[1,2,3], [4,5,6]]).det()
+        * 
+        * @return {number}
+        */
+
+        det(){
+            if(this.isSquare()){
+                if(this.columns === 2){
+                    // 2 x 2 matrix 
+                    var a,b,c,d;
+                    a = this.get(0, 0);
+                    b = this.get(0, 1);
+                    c = this.get(1, 0);
+                    d = this.get(1, 1);
+
+                    return a * d - ( b * c);
+
+                }else if(this.columns === 3){
+                    // 3 x 3 matrix
+                    var subMatrix0, subMatrix1, subMatrix2;
+                    var a, b, c;
+                    
+                    subMatrix0 = this.selection([1, 2], [1, 2]);
+                    subMatrix1 = this.selection([1, 2], [0, 2]);
+                    subMatrix2 = this.selection([1, 2], [0, 1]);
+                    a = this.get(0, 0);
+                    b = this.get(0, 1);
+                    c = this.get(0, 2);
+                    
+                    return a * subMatrix0.det()  - b * subMatrix1.det() + c * subMatrix2.det();
+
+                }else{
+                    // general purpose determinant
+                    
+                    throw Error('Not implemented yet');
+                }
+
+            }else{
+                throw Error('Determinant can only be calculated for a square matrix.');
+            }
+        }
     }
 
     Matrix.prototype.klass = 'Matrix';