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// File: math_EigenValuesSearcher.cxx
// Created: Thu Dec 15 17:58:17 2005
// Author: Julia GERASIMOVA
// <jgv@clubox>
#include <math_EigenValuesSearcher.ixx>
//==========================================================================
//function : pythag
// Computation of sqrt(x*x + y*y).
//==========================================================================
static inline Standard_Real pythag(const Standard_Real x,
const Standard_Real y)
{
return Sqrt(x*x + y*y);
}
math_EigenValuesSearcher::math_EigenValuesSearcher(const TColStd_Array1OfReal& Diagonal,
const TColStd_Array1OfReal& Subdiagonal)
{
myIsDone = Standard_False;
Standard_Integer n = Diagonal.Length();
if (Subdiagonal.Length() != n)
Standard_Failure::Raise("math_EigenValuesSearcher : dimension mismatch");
myDiagonal = new TColStd_HArray1OfReal(1, n);
myDiagonal->ChangeArray1() = Diagonal;
mySubdiagonal = new TColStd_HArray1OfReal(1, n);
mySubdiagonal->ChangeArray1() = Subdiagonal;
myN = n;
myEigenValues = new TColStd_HArray1OfReal(1, n);
myEigenVectors = new TColStd_HArray2OfReal(1, n, 1, n);
Standard_Real* d = new Standard_Real [n+1];
Standard_Real* e = new Standard_Real [n+1];
Standard_Real** z = new Standard_Real* [n+1];
Standard_Integer i, j;
for (i = 1; i <= n; i++)
z[i] = new Standard_Real [n+1];
for (i = 1; i <= n; i++)
d[i] = myDiagonal->Value(i);
for (i = 2; i <= n; i++)
e[i] = mySubdiagonal->Value(i);
for (i = 1; i <= n; i++)
for (j = 1; j <= n; j++)
z[i][j] = (i == j)? 1. : 0.;
Standard_Boolean result;
Standard_Integer m;
Standard_Integer l;
Standard_Integer iter;
//Standard_Integer i;
Standard_Integer k;
Standard_Real s;
Standard_Real r;
Standard_Real p;
Standard_Real g;
Standard_Real f;
Standard_Real dd;
Standard_Real c;
Standard_Real b;
result = Standard_True;
if (n != 1)
{
// Shift e.
for (i = 2; i <= n; i++)
e[i - 1] = e[i];
e[n] = 0.0;
for (l = 1; l <= n; l++) {
iter = 0;
do {
for (m = l; m <= n-1; m++) {
dd = Abs(d[m]) + Abs(d[m + 1]);
if (Abs(e[m]) + dd == dd)
break;
}
if (m != l) {
if (iter++ == 30) {
result = Standard_False;
break; //return result;
}
g = (d[l + 1] - d[l])/(2.*e[l]);
r = pythag(1., g);
if (g < 0)
g = d[m] - d[l] + e[l]/(g - r);
else
g = d[m] - d[l] + e[l]/(g + r);
s = 1.;
c = 1.;
p = 0.;
for (i = m - 1; i >= l; i--) {
f = s*e[i];
b = c*e[i];
r = pythag (f, g);
e[i + 1] = r;
if (r == 0.) {
d[i + 1] -= p;
e[m] = 0.;
break;
}
s = f/r;
c = g/r;
g = d[i + 1] - p;
r = (d[i] - g)*s + 2.0*c*b;
p = s*r;
d[i + 1] = g + p;
g = c*r - b;
for (k = 1; k <= n; k++) {
f = z[k][i + 1];
z[k][i + 1] = s*z[k][i] + c*f;
z[k][i] = c*z[k][i] - s*f;
}
}
if (r == 0 && i >= 1)
continue;
d[l] -= p;
e[l] = g;
e[m] = 0.;
}
}
while (m != l);
if (result == Standard_False)
break;
} //end of for (l = 1; l <= n; l++)
} //end of if (n != 1)
if (result)
{
for (i = 1; i <= n; i++)
myEigenValues->ChangeValue(i) = d[i];
for (i = 1; i <= n; i++)
for (j = 1; j <= n; j++)
myEigenVectors->ChangeValue(i, j) = z[i][j];
}
myIsDone = result;
delete [] d;
delete [] e;
for (i = 1; i <= n; i++)
delete [] z[i];
delete [] z;
}
Standard_Boolean math_EigenValuesSearcher::IsDone() const
{
return myIsDone;
}
Standard_Integer math_EigenValuesSearcher::Dimension() const
{
return myN;
}
Standard_Real math_EigenValuesSearcher::EigenValue(const Standard_Integer Index) const
{
return myEigenValues->Value(Index);
}
math_Vector math_EigenValuesSearcher::EigenVector(const Standard_Integer Index) const
{
math_Vector theVector(1, myN);
Standard_Integer i;
for (i = 1; i <= myN; i++)
theVector(i) = myEigenVectors->Value(i, Index);
return theVector;
}
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