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/*
* 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.
*/
package com.android.inputmethod.keyboard.internal;
import com.android.inputmethod.annotations.UsedForTesting;
import com.android.inputmethod.keyboard.internal.MatrixUtils.MatrixOperationFailedException;
import android.util.Log;
import java.util.Arrays;
/**
* Utilities to smooth coordinates. Currently, we calculate 3d least squares formula by using
* Lagrangian smoothing
*/
@UsedForTesting
public class SmoothingUtils {
private static final String TAG = SmoothingUtils.class.getSimpleName();
private static final boolean DEBUG = false;
private SmoothingUtils() {
// not allowed to instantiate publicly
}
/**
* Find a most likely 3d least squares formula for specified coordinates.
* "retval" should be a 1x4 size matrix.
*/
@UsedForTesting
public static void get3DParameters(final float[] xs, final float[] ys,
final float[][] retval) throws MatrixOperationFailedException {
final int COEFF_COUNT = 4; // Coefficient count for 3d smoothing
if (retval.length != COEFF_COUNT || retval[0].length != 1) {
Log.d(TAG, "--- invalid length of 3d retval " + retval.length + ", "
+ retval[0].length);
return;
}
final int N = xs.length;
// TODO: Never isntantiate the matrix
final float[][] m0 = new float[COEFF_COUNT][COEFF_COUNT];
final float[][] m0Inv = new float[COEFF_COUNT][COEFF_COUNT];
final float[][] m1 = new float[COEFF_COUNT][N];
final float[][] m2 = new float[N][1];
// m0
for (int i = 0; i < COEFF_COUNT; ++i) {
Arrays.fill(m0[i], 0);
for (int j = 0; j < COEFF_COUNT; ++j) {
final int pow = i + j;
for (int k = 0; k < N; ++k) {
m0[i][j] += (float) Math.pow(xs[k], pow);
}
}
}
// m0Inv
MatrixUtils.inverse(m0, m0Inv);
if (DEBUG) {
MatrixUtils.dump("m0-1", m0Inv);
}
// m1
for (int i = 0; i < COEFF_COUNT; ++i) {
for (int j = 0; j < N; ++j) {
m1[i][j] = (i == 0) ? 1.0f : m1[i - 1][j] * xs[j];
}
}
// m2
for (int i = 0; i < N; ++i) {
m2[i][0] = ys[i];
}
final float[][] m0Invxm1 = new float[COEFF_COUNT][N];
if (DEBUG) {
MatrixUtils.dump("a0", m0Inv);
MatrixUtils.dump("a1", m1);
}
MatrixUtils.multiply(m0Inv, m1, m0Invxm1);
if (DEBUG) {
MatrixUtils.dump("a2", m0Invxm1);
MatrixUtils.dump("a3", m2);
}
MatrixUtils.multiply(m0Invxm1, m2, retval);
if (DEBUG) {
MatrixUtils.dump("result", retval);
}
}
}
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