Initial data commit

Task/Gauss-Jordan-matrix-inversion/Java/gauss-jordan-matrix-inversion-1.java

@@ -0,0 +1,22 @@
+// GaussJordan.java
+
+import java.util.Random;
+
+public class GaussJordan {
+    public static void main(String[] args) {
+        int rows = 5;
+        Matrix m = new Matrix(rows, rows);
+        Random r = new Random();
+        for (int row = 0; row < rows; ++row) {
+            for (int column = 0; column < rows; ++column)
+                m.set(row, column, r.nextDouble());
+        }
+        System.out.println("Matrix:");
+        m.print();
+        System.out.println("Inverse:");
+        Matrix inv = m.inverse();
+        inv.print();
+        System.out.println("Product of matrix and inverse:");
+        Matrix.product(m, inv).print();
+    }
+}

Task/Gauss-Jordan-matrix-inversion/Java/gauss-jordan-matrix-inversion-2.java

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+// Matrix.java
+
+public class Matrix {
+    private int rows;
+    private int columns;
+    private double[][] elements;
+
+    public Matrix(int rows, int columns) {
+        this.rows = rows;
+        this.columns = columns;
+        elements = new double[rows][columns];
+    }
+
+    public void set(int row, int column, double value) {
+        elements[row][column] = value;
+    }
+
+    public double get(int row, int column) {
+        return elements[row][column];
+    }
+
+    public void print() {
+        for (int row = 0; row < rows; ++row) {
+            for (int column = 0; column < columns; ++column) {
+                if (column > 0)
+                    System.out.print(' ');
+                System.out.printf("%7.3f", elements[row][column]);
+            }
+            System.out.println();
+        }
+    }
+
+    // Returns the inverse of this matrix
+    public Matrix inverse() {
+        assert(rows == columns);
+        // Augment by identity matrix
+        Matrix tmp = new Matrix(rows, columns * 2);
+        for (int row = 0; row < rows; ++row) {
+            System.arraycopy(elements[row], 0, tmp.elements[row], 0, columns);
+            tmp.elements[row][row + columns] = 1;
+        }
+        tmp.toReducedRowEchelonForm();
+        Matrix inv = new Matrix(rows, columns);
+        for (int row = 0; row < rows; ++row)
+            System.arraycopy(tmp.elements[row], columns, inv.elements[row], 0, columns);
+        return inv;
+    }
+
+    // Converts this matrix into reduced row echelon form
+    public void toReducedRowEchelonForm() {
+        for (int row = 0, lead = 0; row < rows && lead < columns; ++row, ++lead) {
+            int i = row;
+            while (elements[i][lead] == 0) {
+                if (++i == rows) {
+                    i = row;
+                    if (++lead == columns)
+                        return;
+                }
+            }
+            swapRows(i, row);
+            if (elements[row][lead] != 0) {
+                double f = elements[row][lead];
+                for (int column = 0; column < columns; ++column)
+                    elements[row][column] /= f;
+            }
+            for (int j = 0; j < rows; ++j) {
+                if (j == row)
+                    continue;
+                double f = elements[j][lead];
+                for (int column = 0; column < columns; ++column)
+                    elements[j][column] -= f * elements[row][column];
+            }
+        }
+    }
+
+    // Returns the matrix product of a and b
+    public static Matrix product(Matrix a, Matrix b) {
+        assert(a.columns == b.rows);
+        Matrix result = new Matrix(a.rows, b.columns);
+        for (int i = 0; i < a.rows; ++i) {
+            double[] resultRow = result.elements[i];
+            double[] aRow = a.elements[i];
+            for (int j = 0; j < a.columns; ++j) {
+                double[] bRow = b.elements[j];
+                for (int k = 0; k < b.columns; ++k)
+                    resultRow[k] += aRow[j] * bRow[k];
+            }
+        }
+        return result;
+    }
+
+    private void swapRows(int i, int j) {
+        double[] tmp = elements[i];
+        elements[i] = elements[j];
+        elements[j] = tmp;
+    }
+}