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      1 /*
      2  * Copyright (C) 2013 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.inputmethod.keyboard.internal;
     18 
     19 import com.android.inputmethod.annotations.UsedForTesting;
     20 
     21 import android.util.Log;
     22 
     23 import java.util.Arrays;
     24 
     25 /**
     26  * Utilities for matrix operations. Don't instantiate objects inside this class to prevent
     27  * unexpected performance regressions.
     28  */
     29 @UsedForTesting
     30 public class MatrixUtils {
     31     private static final String TAG = MatrixUtils.class.getSimpleName();
     32     public static class MatrixOperationFailedException extends Exception {
     33         private static final long serialVersionUID = 4384485606788583829L;
     34 
     35         public MatrixOperationFailedException(String msg) {
     36             super(msg);
     37             Log.d(TAG, msg);
     38         }
     39     }
     40 
     41     /**
     42      * A utility function to inverse matrix.
     43      * Find a pivot and swap the row of squareMatrix0 and squareMatrix1
     44      */
     45     private static void findPivotAndSwapRow(final int row, final float[][] squareMatrix0,
     46             final float[][] squareMatrix1, final int size) {
     47         int ip = row;
     48         float pivot = Math.abs(squareMatrix0[row][row]);
     49         for (int i = row + 1; i < size; ++i) {
     50             if (pivot < Math.abs(squareMatrix0[i][row])) {
     51                 ip = i;
     52                 pivot = Math.abs(squareMatrix0[i][row]);
     53             }
     54         }
     55         if (ip != row) {
     56             for (int j = 0; j < size; ++j) {
     57                 final float temp0 = squareMatrix0[ip][j];
     58                 squareMatrix0[ip][j] = squareMatrix0[row][j];
     59                 squareMatrix0[row][j] = temp0;
     60                 final float temp1 = squareMatrix1[ip][j];
     61                 squareMatrix1[ip][j] = squareMatrix1[row][j];
     62                 squareMatrix1[row][j] = temp1;
     63             }
     64         }
     65     }
     66 
     67     /**
     68      * A utility function to inverse matrix. This function calculates answer for each row by
     69      * sweeping method of Gauss Jordan elimination
     70      */
     71     private static void sweep(final int row, final float[][] squareMatrix0,
     72             final float[][] squareMatrix1, final int size) throws MatrixOperationFailedException {
     73         final float pivot = squareMatrix0[row][row];
     74         if (pivot == 0) {
     75             throw new MatrixOperationFailedException("Inverse failed. Invalid pivot");
     76         }
     77         for (int j = 0; j < size; ++j) {
     78             squareMatrix0[row][j] /= pivot;
     79             squareMatrix1[row][j] /= pivot;
     80         }
     81         for (int i = 0; i < size; i++) {
     82             final float sweepTargetValue = squareMatrix0[i][row];
     83             if (i != row) {
     84                 for (int j = row; j < size; ++j) {
     85                     squareMatrix0[i][j] -= sweepTargetValue * squareMatrix0[row][j];
     86                 }
     87                 for (int j = 0; j < size; ++j) {
     88                     squareMatrix1[i][j] -= sweepTargetValue * squareMatrix1[row][j];
     89                 }
     90             }
     91         }
     92     }
     93 
     94     /**
     95      * A function to inverse matrix.
     96      * The inverse matrix of squareMatrix will be output to inverseMatrix. Please notice that
     97      * the value of squareMatrix is modified in this function and can't be resuable.
     98      */
     99     @UsedForTesting
    100     public static void inverse(final float[][] squareMatrix,
    101             final float[][] inverseMatrix) throws MatrixOperationFailedException {
    102         final int size = squareMatrix.length;
    103         if (squareMatrix[0].length != size || inverseMatrix.length != size
    104                 || inverseMatrix[0].length != size) {
    105             throw new MatrixOperationFailedException(
    106                     "--- invalid length. column should be 2 times larger than row.");
    107         }
    108         for (int i = 0; i < size; ++i) {
    109             Arrays.fill(inverseMatrix[i], 0.0f);
    110             inverseMatrix[i][i] = 1.0f;
    111         }
    112         for (int i = 0; i < size; ++i) {
    113             findPivotAndSwapRow(i, squareMatrix, inverseMatrix, size);
    114             sweep(i, squareMatrix, inverseMatrix, size);
    115         }
    116     }
    117 
    118     /**
    119      * A matrix operation to multiply m0 and m1.
    120      */
    121     @UsedForTesting
    122     public static void multiply(final float[][] m0, final float[][] m1,
    123             final float[][] retval) throws MatrixOperationFailedException {
    124         if (m0[0].length != m1.length) {
    125             throw new MatrixOperationFailedException(
    126                     "--- invalid length for multiply " + m0[0].length + ", " + m1.length);
    127         }
    128         final int m0h = m0.length;
    129         final int m0w = m0[0].length;
    130         final int m1w = m1[0].length;
    131         if (retval.length != m0h || retval[0].length != m1w) {
    132             throw new MatrixOperationFailedException(
    133                     "--- invalid length of retval " + retval.length + ", " + retval[0].length);
    134         }
    135 
    136         for (int i = 0; i < m0h; i++) {
    137             Arrays.fill(retval[i], 0);
    138             for (int j = 0; j < m1w; j++) {
    139                 for (int k = 0; k < m0w; k++) {
    140                     retval[i][j] += m0[i][k] * m1[k][j];
    141                 }
    142             }
    143         }
    144     }
    145 
    146     /**
    147      * A utility function to dump the specified matrix in a readable way
    148      */
    149     @UsedForTesting
    150     public static void dump(final String title, final float[][] a) {
    151         final int column = a[0].length;
    152         final int row = a.length;
    153         Log.d(TAG, "Dump matrix: " + title);
    154         Log.d(TAG, "/*---------------------");
    155         final StringBuilder sb = new StringBuilder();
    156         for (int i = 0; i < row; ++i) {
    157             sb.setLength(0);
    158             for (int j = 0; j < column; ++j) {
    159                 sb.append(String.format("%4f", a[i][j])).append(' ');
    160             }
    161             Log.d(TAG, sb.toString());
    162         }
    163         Log.d(TAG, "---------------------*/");
    164     }
    165 }
    166