Calculates the "minimum" cosine distance between two instances. - Android java.lang

Android examples for java.lang:Math Trigonometric Function

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Description

Calculates the "minimum" cosine distance between two instances.

Demo Code

/*//from  w  ww  .jav  a 2  s . com
 * Copyright (C) 2008-2009 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.graphics.RectF;
import android.util.Log;
import java.util.ArrayList;
import java.util.Arrays;
import java.io.Closeable;
import java.io.IOException;

public class Main{
    /**
     * Calculates the "minimum" cosine distance between two instances.
     * 
     * @param vector1
     * @param vector2
     * @param numOrientations the maximum number of orientation allowed
     * @return the distance between the two instances (between 0 and Math.PI)
     */
    static float minimumCosineDistance(float[] vector1, float[] vector2,
            int numOrientations) {
        final int len = vector1.length;
        float a = 0;
        float b = 0;
        for (int i = 0; i < len; i += 2) {
            a += vector1[i] * vector2[i] + vector1[i + 1] * vector2[i + 1];
            b += vector1[i] * vector2[i + 1] - vector1[i + 1] * vector2[i];
        }
        if (a != 0) {
            final float tan = b / a;
            final double angle = Math.atan(tan);
            if (numOrientations > 2
                    && Math.abs(angle) >= Math.PI / numOrientations) {
                return (float) Math.acos(a);
            } else {
                final double cosine = Math.cos(angle);
                final double sine = cosine * tan;
                return (float) Math.acos(a * cosine + b * sine);
            }
        } else {
            return (float) Math.PI / 2;
        }
    }
}

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