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      1 /*
      2  * Copyright (C) 2014 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 #ifndef LATINIME_NORMAL_DISTRIBUTION_2D_H
     18 #define LATINIME_NORMAL_DISTRIBUTION_2D_H
     19 
     20 #include <cmath>
     21 
     22 #include "defines.h"
     23 #include "suggest/core/layout/geometry_utils.h"
     24 #include "suggest/core/layout/normal_distribution.h"
     25 
     26 namespace latinime {
     27 
     28 // Normal distribution on a 2D plane. The covariance is always zero, but the distribution can be
     29 // rotated.
     30 class NormalDistribution2D {
     31  public:
     32     NormalDistribution2D(const float uX, const float sigmaX, const float uY, const float sigmaY,
     33             const float theta)
     34             : mXDistribution(0.0f, sigmaX), mYDistribution(0.0f, sigmaY), mUX(uX), mUY(uY),
     35               mSinTheta(sinf(theta)), mCosTheta(cosf(theta)) {}
     36 
     37     float getProbabilityDensity(const float x, const float y) const {
     38         // Shift
     39         const float shiftedX = x - mUX;
     40         const float shiftedY = y - mUY;
     41         // Rotate
     42         const float rotatedShiftedX = mCosTheta * shiftedX + mSinTheta * shiftedY;
     43         const float rotatedShiftedY = -mSinTheta * shiftedX + mCosTheta * shiftedY;
     44         return mXDistribution.getProbabilityDensity(rotatedShiftedX)
     45                 * mYDistribution.getProbabilityDensity(rotatedShiftedY);
     46     }
     47 
     48  private:
     49     DISALLOW_IMPLICIT_CONSTRUCTORS(NormalDistribution2D);
     50 
     51     const NormalDistribution mXDistribution;
     52     const NormalDistribution mYDistribution;
     53     const float mUX;
     54     const float mUY;
     55     const float mSinTheta;
     56     const float mCosTheta;
     57 };
     58 } // namespace latinime
     59 #endif // LATINIME_NORMAL_DISTRIBUTION_2D_H
     60