Matrix substraction added, and renamed the test calss for it and the Matrix Addition

src/main/java/com/ugsbo/matrixcalc/MatrixCalcMath.java

@@ -31,7 +31,7 @@ public class MatrixCalcMath {
             return result;
         } else {
             return null;
-            //throw new IllegalArgumentException("Matricies must be linked");
+            // throw new IllegalArgumentException("Matricies must be linked");
         }
     }
 
@@ -97,4 +97,29 @@ public class MatrixCalcMath {
         }
 
     }
+
+    /**
+     * Substracts matrix A by the matrix B. Substaction for Matrices is just the
+     * substraction of each component with thier coorsponding component.
+     * 
+     * @param matrixA The Inputmatrix A (right TextArea in the GUI)
+     * @param matrixB The Inputmatrix B (left TextArea in the GUI
+     * @return matrix A substracted by matrix B
+     */
+    public double[][] matrixSubstraction(double[][] matrixA, double[][] matrixB) {
+        if (checkIfMatriciesAreTheSameDimension(matrixA, matrixB)) {
+            double[][] result = new double[matrixA.length][matrixA[0].length];
+            for (int rows = 0; rows < matrixA.length; rows++) {
+                for (int colums = 0; colums < matrixA[0].length; colums++) {
+                    result[rows][colums] = matrixA[rows][colums] - matrixB[rows][colums];
+                }
+            }
+            return result;
+        } else {
+            return null;
+            // TODO Fragen wie man eine Exception testen kann.
+            // throw new IllegalArgumentException("Matricies need to have the same
+            // Dimensions");
+        }
+    }
 }

src/test/java/com/ugsbo/matrixcalc/MatrixAdditionTest.java → src/test/java/com/ugsbo/matrixcalc/MatrixAdditionAndSubstractionTest.java

@@ -7,9 +7,9 @@ import static org.junit.Assert.assertTrue;
 import org.junit.Test;
 
 /**
- * Tests the funktionality to add two matricies
+ * Tests the funktionality to add and substract two matricies
  */
-public class MatrixAdditionTest {
+public class MatrixAdditionAndSubstractionTest {
 
     @Test
     public void twoMatriciesHaveTheSameDimensions() {
@@ -58,4 +58,43 @@ public class MatrixAdditionTest {
         assertArrayEquals("The first row is not correct", matrixC[0], result[0], 0.1);
         assertArrayEquals("The seound row is not correct", matrixC[1], result[1], 0.1);
     }
+
+    @Test
+    public void substractTwoMatriciesWithSameContent() {
+        MatrixCalcMath math = new MatrixCalcMath();
+        double[][] matrixA = { { 1.0, 1.0 }, { 1.0, 1.0 } };
+        double[][] matrixB = { { 1.0, 1.0 }, { 1.0, 1.0 } };
+        double[][] matrixC = { { 0.0, 0.0 }, { 0.0, 0.0 } };
+
+        double[][] result = math.matrixSubstraction(matrixA, matrixB);
+
+        assertArrayEquals("The first row is not correct", matrixC[0], result[0], 0.1);
+        assertArrayEquals("The seound row is not correct", matrixC[1], result[1], 0.1);
+    }
+
+    @Test
+    public void substractTwoMatriciesWithDiffrentContent() {
+        MatrixCalcMath math = new MatrixCalcMath();
+        double[][] matrixA = { { 1.0, 2.0 }, { 3.0, 4.0 } };
+        double[][] matrixB = { { 5.0, 6.0 }, { 7.0, 8.0 } };
+        double[][] matrixC = { { -4.0, -4.0 }, { -4.0, -4.0 } };
+
+        double[][] result = math.matrixSubstraction(matrixA, matrixB);
+
+        assertArrayEquals("The first row is not correct", matrixC[0], result[0], 0.1);
+        assertArrayEquals("The seound row is not correct", matrixC[1], result[1], 0.1);
+    }
+
+    @Test
+    public void substractTwoMatriciesWithNegativeContent() {
+        MatrixCalcMath math = new MatrixCalcMath();
+        double[][] matrixA = { { -1.0, -2.0 }, { -3.0, -4.0 } };
+        double[][] matrixB = { { 5.0, 6.0 }, { 7.0, 8.0 } };
+        double[][] matrixC = { { -6.0, -8.0 }, { -10.0, -12.0 } };
+
+        double[][] result = math.matrixSubstraction(matrixA, matrixB);
+
+        assertArrayEquals("The first row is not correct", matrixC[0], result[0], 0.1);
+        assertArrayEquals("The seound row is not correct", matrixC[1], result[1], 0.1);
+    }
 }