diff --git a/src/main/java/com/thealgorithms/matrix/StochasticMatrix.java b/src/main/java/com/thealgorithms/matrix/StochasticMatrix.java new file mode 100644 index 000000000000..8b071113f9cc --- /dev/null +++ b/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"); + } + } +} diff --git a/src/test/java/com/thealgorithms/matrix/StochasticMatrixTest.java b/src/test/java/com/thealgorithms/matrix/StochasticMatrixTest.java new file mode 100644 index 000000000000..1bba918dadac --- /dev/null +++ b/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)); + } +}