1 /* 2 * Copyright 2015 The Etc2Comp Authors. 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 #include "EtcConfig.h" 18 #include "EtcMath.h" 19 20 namespace Etc 21 { 22 23 // ---------------------------------------------------------------------------------------------------- 24 // calculate the line that best fits the set of XY points contained in a_afX[] and a_afY[] 25 // use a_fSlope and a_fOffset to define that line 26 // Regression(float a_afX[],float a_afY[],unsigned int a_Points,float * a_fSlope,float * a_fOffset)27 bool Regression(float a_afX[], float a_afY[], unsigned int a_Points, 28 float *a_fSlope, float *a_fOffset) 29 { 30 float fPoints = (float)a_Points; 31 32 float fSumX = 0.0f; 33 float fSumY = 0.0f; 34 float fSumXY = 0.0f; 35 float fSumX2 = 0.0f; 36 37 for (unsigned int uiPoint = 0; uiPoint < a_Points; uiPoint++) 38 { 39 fSumX += a_afX[uiPoint]; 40 fSumY += a_afY[uiPoint]; 41 fSumXY += a_afX[uiPoint] * a_afY[uiPoint]; 42 fSumX2 += a_afX[uiPoint] * a_afX[uiPoint]; 43 } 44 45 float fDivisor = fPoints*fSumX2 - fSumX*fSumX; 46 47 // if vertical line 48 if (fDivisor == 0.0f) 49 { 50 *a_fSlope = 0.0f; 51 *a_fOffset = 0.0f; 52 return true; 53 } 54 55 *a_fSlope = (fPoints*fSumXY - fSumX*fSumY) / fDivisor; 56 *a_fOffset = (fSumY - (*a_fSlope)*fSumX) / fPoints; 57 58 return false; 59 } 60 61 // ---------------------------------------------------------------------------------------------------- 62 // 63 64 } // namespace Etc 65