GeomPropagators/src/RealQuadEquation.h

0001 #ifndef RealQuadEquation_H
0002 #define RealQuadEquation_H
0003
0004 #include <cmath>
0005 #include "FWCore/Utilities/interface/Visibility.h"
0006
0007 /** A numericaly stable and as fast as can be quadratic equation solver.
0008  *  The equation has the form A*x^2 + B*x + C = 0
0009  */
0010
0011 struct dso_internal RealQuadEquation {
0012   double first;
0013   double second;
0014   bool hasSolution;
0015
0016   RealQuadEquation(double A, double B, double C) {
0017     double D = B * B - 4 * A * C;
0018     if (D < 0)
0019       hasSolution = false;
0020     else {
0021       hasSolution = true;
0022       auto q = -0.5 * (B + std::copysign(std::sqrt(D), B));
0023       first = q / A;
0024       second = C / q;
0025     }
0026   }
0027 };
0028
0029 #endif