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- /*
- * Copyright 2015 The Etc2Comp Authors.
- *
- * 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.
- */
- #include "EtcConfig.h"
- #include "EtcMath.h"
- namespace Etc
- {
- // ----------------------------------------------------------------------------------------------------
- // calculate the line that best fits the set of XY points contained in a_afX[] and a_afY[]
- // use a_fSlope and a_fOffset to define that line
- //
- bool Regression(float a_afX[], float a_afY[], unsigned int a_Points,
- float *a_fSlope, float *a_fOffset)
- {
- float fPoints = (float)a_Points;
- float fSumX = 0.0f;
- float fSumY = 0.0f;
- float fSumXY = 0.0f;
- float fSumX2 = 0.0f;
- for (unsigned int uiPoint = 0; uiPoint < a_Points; uiPoint++)
- {
- fSumX += a_afX[uiPoint];
- fSumY += a_afY[uiPoint];
- fSumXY += a_afX[uiPoint] * a_afY[uiPoint];
- fSumX2 += a_afX[uiPoint] * a_afX[uiPoint];
- }
- float fDivisor = fPoints*fSumX2 - fSumX*fSumX;
- // if vertical line
- if (fDivisor == 0.0f)
- {
- *a_fSlope = 0.0f;
- *a_fOffset = 0.0f;
- return true;
- }
- *a_fSlope = (fPoints*fSumXY - fSumX*fSumY) / fDivisor;
- *a_fOffset = (fSumY - (*a_fSlope)*fSumX) / fPoints;
- return false;
- }
- // ----------------------------------------------------------------------------------------------------
- //
- } // namespace Etc
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