94 lines
3.2 KiB
Java
94 lines
3.2 KiB
Java
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import java.util.Arrays;
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public class MatrixDemo {
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public static final class Matrix {
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private final int rows;
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private final int cols;
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private final double[][] a;
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public Matrix(double[][] data) {
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if (data == null || data.length == 0 || data[0].length == 0)
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throw new IllegalArgumentException("Matrix cannot have zero dimension");
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this.rows = data.length;
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this.cols = data[0].length;
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this.a = new double[rows][cols];
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for (int i = 0; i < rows; i++) {
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if (data[i].length != cols)
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throw new IllegalArgumentException("Jagged arrays are not allowed");
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System.arraycopy(data[i], 0, this.a[i], 0, cols);
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}
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}
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public int rows() { return rows; }
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public int cols() { return cols; }
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public static Matrix identity(int n) {
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if (n < 1) throw new IllegalArgumentException("Size of identity matrix can't be less than 1");
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double[][] id = new double[n][n];
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for (int i = 0; i < n; i++) id[i][i] = 1.0;
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return new Matrix(id);
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}
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public Matrix multiply(Matrix other) {
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if (this.cols != other.rows)
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throw new IllegalArgumentException("Matrices cannot be multiplied: " +
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this.rows + "x" + this.cols + " * " + other.rows + "x" + other.cols);
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double[][] r = new double[this.rows][other.cols];
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for (int i = 0; i < this.rows; i++) {
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for (int k = 0; k < this.cols; k++) {
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double v = this.a[i][k];
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if (v == 0) continue;
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for (int j = 0; j < other.cols; j++) {
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r[i][j] += v * other.a[k][j];
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}
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}
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}
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return new Matrix(r);
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}
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public Matrix pow(int n) {
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if (rows != cols) throw new IllegalStateException("Not a square matrix");
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if (n < 0) throw new IllegalArgumentException("Negative exponents not supported");
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if (n == 0) return identity(rows);
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if (n == 1) return this;
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Matrix result = identity(rows);
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Matrix base = this;
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int e = n;
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while (e > 0) {
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if ((e & 1) == 1) result = result.multiply(base);
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e >>= 1;
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if (e > 0) base = base.multiply(base);
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}
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return result;
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}
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@Override
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public String toString() {
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StringBuilder sb = new StringBuilder();
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sb.append('[');
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for (int i = 0; i < rows; i++) {
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sb.append(Arrays.toString(a[i]));
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if (i < rows - 1) sb.append('\n');
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}
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sb.append(']');
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return sb.toString();
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}
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}
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public static void main(String[] args) {
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Matrix m = new Matrix(new double[][] {
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{3, 2},
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{2, 1}
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});
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for (int i = 0; i <= 10; i++) {
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System.out.println("** Power of " + i + " **");
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System.out.println(m.pow(i));
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System.out.println();
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}
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}
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}
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