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_H 18 #define LATINIME_NORMAL_DISTRIBUTION_H 19 20 #include <cmath> 21 22 #include "defines.h" 23 24 namespace latinime { 25 26 // Normal distribution N(u, sigma^2). 27 class NormalDistribution { 28 public: 29 NormalDistribution(const float u, const float sigma) 30 : mU(u), 31 mPreComputedNonExpPart(1.0f / sqrtf(2.0f * M_PI_F 32 * GeometryUtils::SQUARE_FLOAT(sigma))), 33 mPreComputedExponentPart(-1.0f / (2.0f * GeometryUtils::SQUARE_FLOAT(sigma))) {} 34 35 float getProbabilityDensity(const float x) const { 36 const float shiftedX = x - mU; 37 return mPreComputedNonExpPart 38 * expf(mPreComputedExponentPart * GeometryUtils::SQUARE_FLOAT(shiftedX)); 39 } 40 41 private: 42 DISALLOW_IMPLICIT_CONSTRUCTORS(NormalDistribution); 43 44 const float mU; // mean value 45 const float mPreComputedNonExpPart; // = 1 / sqrt(2 * PI * sigma^2) 46 const float mPreComputedExponentPart; // = -1 / (2 * sigma^2) 47 }; 48 } // namespace latinime 49 #endif // LATINIME_NORMAL_DISTRIBUTION_H 50
