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.

Author: Dsannue

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

@@ -0,0 +1,74 @@
+package com.thealgorithms.maths;
+
+/**
+ * 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.
+ */
+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");
+        }
+    }
+}