65 lines
1.8 KiB
C++
65 lines
1.8 KiB
C++
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/*
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* Copyright 2015 The Etc2Comp Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "EtcConfig.h"
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#include "EtcMath.h"
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namespace Etc
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{
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// ----------------------------------------------------------------------------------------------------
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// calculate the line that best fits the set of XY points contained in a_afX[] and a_afY[]
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// use a_fSlope and a_fOffset to define that line
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//
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bool Regression(float a_afX[], float a_afY[], unsigned int a_Points,
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float *a_fSlope, float *a_fOffset)
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{
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float fPoints = (float)a_Points;
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float fSumX = 0.0f;
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float fSumY = 0.0f;
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float fSumXY = 0.0f;
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float fSumX2 = 0.0f;
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for (unsigned int uiPoint = 0; uiPoint < a_Points; uiPoint++)
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{
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fSumX += a_afX[uiPoint];
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fSumY += a_afY[uiPoint];
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fSumXY += a_afX[uiPoint] * a_afY[uiPoint];
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fSumX2 += a_afX[uiPoint] * a_afX[uiPoint];
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}
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float fDivisor = fPoints*fSumX2 - fSumX*fSumX;
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// if vertical line
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if (fDivisor == 0.0f)
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{
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*a_fSlope = 0.0f;
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*a_fOffset = 0.0f;
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return true;
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}
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*a_fSlope = (fPoints*fSumXY - fSumX*fSumY) / fDivisor;
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*a_fOffset = (fSumY - (*a_fSlope)*fSumX) / fPoints;
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return false;
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}
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// ----------------------------------------------------------------------------------------------------
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//
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} // namespace Etc
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