Add matrix multiplication with double[][] and unit tests (#6417)

* MatrixMultiplication.java created and updated. * Add necessary comment to MatrixMultiplication.java * Create MatrixMultiplicationTest.java * method for 2 by 2 matrix multiplication is created * Use assertMatrixEquals(), otherwise there can be error due to floating point arithmetic errors * assertMatrixEquals method created and updated * method created for 3by2 matrix multiply with 2by1 matrix * method created for null matrix multiplication * method for test matrix dimension error * method for test empty matrix input * testMultiply3by2and2by1 test case updated * Check for empty matrices part updated * Updated Unit test coverage * files updated * clean the code * clean the code * Updated files with google-java-format * Updated files * Updated files * Updated files * Updated files * Add reference links and complexities * Add test cases for 1by1 matrix and non-rectangular matrix * Add reference links and complexities --------- Co-authored-by: Deniz Altunkapan <93663085+DenizAltunkapan@users.noreply.github.com>
2025-12-19 07:00:35 +08:00 · 2025-07-21 21:37:13 +05:30
parent 2722b0ecc9
commit 2dfad7ef8f
2 changed files with 170 additions and 0 deletions
--- a/src/test/java/com/thealgorithms/matrix/MatrixMultiplicationTest.java
+++ b/src/test/java/com/thealgorithms/matrix/MatrixMultiplicationTest.java
@@ -0,0 +1,101 @@
+package com.thealgorithms.matrix;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+public class MatrixMultiplicationTest {
+
+    private static final double EPSILON = 1e-9; // for floating point comparison
+
+    @Test
+    void testMultiply1by1() {
+        double[][] matrixA = {{1.0}};
+        double[][] matrixB = {{2.0}};
+        double[][] expected = {{2.0}};
+
+        double[][] result = MatrixMultiplication.multiply(matrixA, matrixB);
+        assertMatrixEquals(expected, result);
+    }
+
+    @Test
+    void testMultiply2by2() {
+        double[][] matrixA = {{1.0, 2.0}, {3.0, 4.0}};
+        double[][] matrixB = {{5.0, 6.0}, {7.0, 8.0}};
+        double[][] expected = {{19.0, 22.0}, {43.0, 50.0}};
+
+        double[][] result = MatrixMultiplication.multiply(matrixA, matrixB);
+        assertMatrixEquals(expected, result); // Use custom method due to floating point issues
+    }
+
+    @Test
+    void testMultiply3by2and2by1() {
+        double[][] matrixA = {{1.0, 2.0}, {3.0, 4.0}, {5.0, 6.0}};
+        double[][] matrixB = {{7.0}, {8.0}};
+        double[][] expected = {{23.0}, {53.0}, {83.0}};
+
+        double[][] result = MatrixMultiplication.multiply(matrixA, matrixB);
+        assertMatrixEquals(expected, result);
+    }
+
+    @Test
+    void testMultiplyNonRectangularMatrices() {
+        double[][] matrixA = {{1.0, 2.0, 3.0}, {4.0, 5.0, 6.0}};
+        double[][] matrixB = {{7.0, 8.0}, {9.0, 10.0}, {11.0, 12.0}};
+        double[][] expected = {{58.0, 64.0}, {139.0, 154.0}};
+
+        double[][] result = MatrixMultiplication.multiply(matrixA, matrixB);
+        assertMatrixEquals(expected, result);
+    }
+
+    @Test
+    void testNullMatrixA() {
+        double[][] b = {{1, 2}, {3, 4}};
+        assertThrows(IllegalArgumentException.class, () -> MatrixMultiplication.multiply(null, b));
+    }
+
+    @Test
+    void testNullMatrixB() {
+        double[][] a = {{1, 2}, {3, 4}};
+        assertThrows(IllegalArgumentException.class, () -> MatrixMultiplication.multiply(a, null));
+    }
+
+    @Test
+    void testMultiplyNull() {
+        double[][] matrixA = {{1.0, 2.0}, {3.0, 4.0}};
+        double[][] matrixB = null;
+
+        Exception exception = assertThrows(IllegalArgumentException.class, () -> MatrixMultiplication.multiply(matrixA, matrixB));
+
+        String expectedMessage = "Input matrices cannot be null";
+        String actualMessage = exception.getMessage();
+
+        assertTrue(actualMessage.contains(expectedMessage));
+    }
+
+    @Test
+    void testIncompatibleDimensions() {
+        double[][] a = {{1.0, 2.0}};
+        double[][] b = {{1.0, 2.0}};
+        assertThrows(IllegalArgumentException.class, () -> MatrixMultiplication.multiply(a, b));
+    }
+
+    @Test
+    void testEmptyMatrices() {
+        double[][] a = new double[0][0];
+        double[][] b = new double[0][0];
+        assertThrows(IllegalArgumentException.class, () -> MatrixMultiplication.multiply(a, b));
+    }
+
+    private void assertMatrixEquals(double[][] expected, double[][] actual) {
+        assertEquals(expected.length, actual.length, "Row count mismatch");
+        for (int i = 0; i < expected.length; i++) {
+            assertEquals(expected[i].length, actual[i].length, "Column count mismatch at row " + i);
+            for (int j = 0; j < expected[i].length; j++) {
+                assertEquals(expected[i][j], actual[i][j], EPSILON, "Mismatch at (" + i + "," + j + ")");
+            }
+        }
+    }
+}