Adding method to check wether a matrix is stochastic (#7184)

* Add StochasticMatrix utility class

This class provides methods to check if a matrix is row-stochastic or column-stochastic, ensuring all elements are non-negative and the sums of rows or columns equal 1.

* Change package from maths to matrix

Updated package declaration for StochasticMatrix class.

* Change package declaration in StochasticMatrixTest

* Delete src/test/java/com/thealgorithms/StochasticMatrixTest.java

* Refactor matrix initialization for test cases

* Fix formatting of matrix initialization in tests

* Remove unnecessary newline in StochasticMatrix

* Add import statement for JUnit in StochasticMatrixTest

* Add additional assertions to StochasticMatrixTest

* Clean up import statements in StochasticMatrixTest

Removed unused import statements for cleaner code.

* Reorder import statements in StochasticMatrixTest

* Remove unused import assertThrows from StochasticMatrixTest

Removed unused import for assertThrows.

Author: Dsannue

src/main/java/com/thealgorithms/matrix/StochasticMatrix.java

@@ -0,0 +1,74 @@
+package com.thealgorithms.matrix;
+
+/**
+ * Utility class to check whether a matrix is stochastic.
+ * A matrix is stochastic if all its elements are non-negative
+ * and the sum of each row or column is equal to 1.
+ *Reference: https://en.wikipedia.org/wiki/Stochastic_matrix
+ */
+public final class StochasticMatrix {
+
+    private static final double TOLERANCE = 1e-9;
+
+    private StochasticMatrix() {
+        // Utility class
+    }
+    /**
+     * Checks if a matrix is row-stochastic.
+     *
+     * @param matrix the matrix to check
+     * @return true if the matrix is row-stochastic
+     * @throws IllegalArgumentException if matrix is null or empty
+     */
+    public static boolean isRowStochastic(double[][] matrix) {
+        validateMatrix(matrix);
+
+        for (double[] row : matrix) {
+            double sum = 0.0;
+            for (double value : row) {
+                if (value < 0) {
+                    return false;
+                }
+                sum += value;
+            }
+            if (Math.abs(sum - 1.0) > TOLERANCE) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /**
+     * Checks if a matrix is column-stochastic.
+     *
+     * @param matrix the matrix to check
+     * @return true if the matrix is column-stochastic
+     * @throws IllegalArgumentException if matrix is null or empty
+     */
+    public static boolean isColumnStochastic(double[][] matrix) {
+        validateMatrix(matrix);
+
+        int rows = matrix.length;
+        int cols = matrix[0].length;
+
+        for (int j = 0; j < cols; j++) {
+            double sum = 0.0;
+            for (int i = 0; i < rows; i++) {
+                if (matrix[i][j] < 0) {
+                    return false;
+                }
+                sum += matrix[i][j];
+            }
+            if (Math.abs(sum - 1.0) > TOLERANCE) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    private static void validateMatrix(double[][] matrix) {
+        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
+            throw new IllegalArgumentException("Matrix must not be null or empty");
+        }
+    }
+}

src/test/java/com/thealgorithms/matrix/StochasticMatrixTest.java

@@ -0,0 +1,28 @@
+package com.thealgorithms.matrix;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+class StochasticMatrixTest {
+
+    @Test
+    void testRowStochasticMatrix() {
+        double[][] matrix = {{0.2, 0.5, 0.3}, {0.1, 0.6, 0.3}};
+        assertTrue(StochasticMatrix.isRowStochastic(matrix));
+        assertFalse(StochasticMatrix.isColumnStochastic(matrix));
+    }
+
+    @Test
+    void testColumnStochasticMatrix() {
+        double[][] matrix = {{0.4, 0.2}, {0.6, 0.8}};
+        assertTrue(StochasticMatrix.isColumnStochastic(matrix));
+    }
+
+    @Test
+    void testInvalidMatrix() {
+        double[][] matrix = {{0.5, -0.5}, {0.5, 1.5}};
+        assertFalse(StochasticMatrix.isRowStochastic(matrix));
+    }
+}