A function to inverse matrix. - Android java.lang

Android examples for java.lang:Math Matrix

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Description

A function to inverse matrix.

Demo Code

/*/*from w w  w .ja v  a 2  s. c o m*/
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import android.util.Log;
import java.util.Arrays;

public class Main{
    /**
     * A function to inverse matrix.
     * The inverse matrix of squareMatrix will be output to inverseMatrix. Please notice that
     * the value of squareMatrix is modified in this function and can't be resuable.
     */

    public static void inverse(final float[][] squareMatrix,
            final float[][] inverseMatrix)
            throws MatrixOperationFailedException {
        final int size = squareMatrix.length;
        if (squareMatrix[0].length != size || inverseMatrix.length != size
                || inverseMatrix[0].length != size) {
            throw new MatrixOperationFailedException(
                    "--- invalid length. column should be 2 times larger than row.");
        }
        for (int i = 0; i < size; ++i) {
            Arrays.fill(inverseMatrix[i], 0.0f);
            inverseMatrix[i][i] = 1.0f;
        }
        for (int i = 0; i < size; ++i) {
            findPivotAndSwapRow(i, squareMatrix, inverseMatrix, size);
            sweep(i, squareMatrix, inverseMatrix, size);
        }
    }
    /**
     * A utility function to inverse matrix.
     * Find a pivot and swap the row of squareMatrix0 and squareMatrix1
     */
    private static void findPivotAndSwapRow(final int row,
            final float[][] squareMatrix0, final float[][] squareMatrix1,
            final int size) {
        int ip = row;
        float pivot = Math.abs(squareMatrix0[row][row]);
        for (int i = row + 1; i < size; ++i) {
            if (pivot < Math.abs(squareMatrix0[i][row])) {
                ip = i;
                pivot = Math.abs(squareMatrix0[i][row]);
            }
        }
        if (ip != row) {
            for (int j = 0; j < size; ++j) {
                final float temp0 = squareMatrix0[ip][j];
                squareMatrix0[ip][j] = squareMatrix0[row][j];
                squareMatrix0[row][j] = temp0;
                final float temp1 = squareMatrix1[ip][j];
                squareMatrix1[ip][j] = squareMatrix1[row][j];
                squareMatrix1[row][j] = temp1;
            }
        }
    }
    /**
     * A utility function to inverse matrix. This function calculates answer for each row by
     * sweeping method of Gauss Jordan elimination
     */
    private static void sweep(final int row, final float[][] squareMatrix0,
            final float[][] squareMatrix1, final int size)
            throws MatrixOperationFailedException {
        final float pivot = squareMatrix0[row][row];
        if (pivot == 0) {
            throw new MatrixOperationFailedException(
                    "Inverse failed. Invalid pivot");
        }
        for (int j = 0; j < size; ++j) {
            squareMatrix0[row][j] /= pivot;
            squareMatrix1[row][j] /= pivot;
        }
        for (int i = 0; i < size; i++) {
            final float sweepTargetValue = squareMatrix0[i][row];
            if (i != row) {
                for (int j = row; j < size; ++j) {
                    squareMatrix0[i][j] -= sweepTargetValue
                            * squareMatrix0[row][j];
                }
                for (int j = 0; j < size; ++j) {
                    squareMatrix1[i][j] -= sweepTargetValue
                            * squareMatrix1[row][j];
                }
            }
        }
    }
}

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