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// File: math_ComputeGaussPointsAndWeights.cxx
// Created: Mon Dec 19 16:01:53 2005
// Author: Julia GERASIMOVA
// <jgv@clubox>
#include <math_ComputeGaussPointsAndWeights.ixx>
#include <math_EigenValuesSearcher.hxx>
#include <math_Array1OfValueAndWeight.hxx>
#include <math_CompareOfValueAndWeight.hxx>
#include <math_QuickSortOfValueAndWeight.hxx>
#include <Standard_ErrorHandler.hxx>
math_ComputeGaussPointsAndWeights::math_ComputeGaussPointsAndWeights(const Standard_Integer Number)
{
myIsDone = Standard_False;
try {
myPoints = new TColStd_HArray1OfReal(1, Number);
myWeights = new TColStd_HArray1OfReal(1, Number);
Standard_Integer i;
TColStd_Array1OfReal aDiag(1, Number);
TColStd_Array1OfReal aSubDiag(1, Number);
//Initialization of a real symmetric tridiagonal matrix for
//computation of Gauss quadrature.
for (i = 1; i <= Number; i++) {
aDiag(i) = 0.;
if (i == 1)
aSubDiag(i) = 0.;
else {
Standard_Integer sqrIm1 = (i-1)*(i-1);
aSubDiag(i) = sqrIm1/(4.*sqrIm1 - 1);
aSubDiag(i) = Sqrt(aSubDiag(i));
}
}
// Compute eigen values.
math_EigenValuesSearcher EVsearch(aDiag, aSubDiag);
if (EVsearch.IsDone()) {
math_Array1OfValueAndWeight VWarray(1, Number);
for (i = 1; i <= Number; i++) {
math_Vector anEigenVector = EVsearch.EigenVector(i);
Standard_Real aWeight = anEigenVector(1);
aWeight = 2. * aWeight * aWeight;
math_ValueAndWeight EVW( EVsearch.EigenValue(i), aWeight );
VWarray(i) = EVW;
}
math_CompareOfValueAndWeight theComparator;
math_QuickSortOfValueAndWeight::Sort(VWarray, theComparator);
for (i = 1; i <= Number; i++) {
myPoints->ChangeValue(i) = VWarray(i).Value();
myWeights->ChangeValue(i) = VWarray(i).Weight();
}
myIsDone = Standard_True;
}
} catch (Standard_Failure) {
}
}
Standard_Boolean math_ComputeGaussPointsAndWeights::IsDone() const
{
return myIsDone;
}
math_Vector math_ComputeGaussPointsAndWeights::Points() const
{
Standard_Integer Number = myPoints->Length();
math_Vector thePoints(1, Number);
for (Standard_Integer i = 1; i <= Number; i++)
thePoints(i) = myPoints->Value(i);
return thePoints;
}
math_Vector math_ComputeGaussPointsAndWeights::Weights() const
{
Standard_Integer Number = myWeights->Length();
math_Vector theWeights(1, Number);
for (Standard_Integer i = 1; i <= Number; i++)
theWeights(i) = myWeights->Value(i);
return theWeights;
}
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