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lanczos: first working version

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Jiri Pittner
2025-12-12 15:54:32 +01:00
parent 7e90168443
commit 1965f4f653
2 changed files with 120 additions and 51 deletions
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67
t.cc
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@@ -4502,9 +4502,44 @@ cout <<"Error = "<<(xt-y).norm()<<endl;
if(0)
{
int n,m;
bool which;
cin>>n >>m >>which;
NRSMat<double> a(n);
NRVec<double> rr(n);
for(int i=0;i<n;++i) for(int j=0;j<=i;++j)
{
a(i,j)= RANDDOUBLE();
if(i==j) a(i,i)+= .5*(i-n*.5);
}
NRSMat<double> aa;
NRMat<double> vv(n,n);
aa=a; diagonalize(aa,rr,&vv);
NRVec<double> r(m);
NRVec<double> *eivecs = new NRVec<double>[m];
cout <<"Exact energies " <<rr<<endl;
if(which) lanczos(a,r,eivecs,NULL,m,1,1e-6,1,200,300);
else davidson(a,r,eivecs,NULL,m,1,1e-6,1,200,300);
cout <<"Iterative energies " <<r;
cout <<"Eigenvectors compare:\n";
for(int i=0; i<m; ++i)
{
cout <<eivecs[i];
for(int j=0; j<n;++j) cout <<vv[j][i]<<" ";
cout <<endl;
}
}
if(1)
{
//n must not be too small
int n,m;
cin>>n >>m;
bool which;
cin>>n >>m>>which ;
NRSMat<complex<double> > a(n);
a.randomize(.1);
@@ -4522,9 +4557,10 @@ cout <<"Exact energies "<<rr;
NRVec<complex<double> > r(m);
NRVec<complex<double> > *eivecs = new NRVec<complex<double> >[m];
davidson(a,r,eivecs,NULL,m,true,1e-5,true,10*n,n);
if(which) lanczos(a,r,eivecs,NULL,m,true,1e-5,true,10*n,n);
else davidson(a,r,eivecs,NULL,m,true,1e-5,true,10*n,n);
cout <<"Davidson energies " <<r;
cout <<"Davidson/Lanczos energies " <<r;
cout <<"Exact energies "<<rr;
cout <<"Eigenvectors compare:\n";
@@ -4537,29 +4573,4 @@ for(int i=0; i<m; ++i)
}
if(1)
{
int n,m;
cin>>n >>m;
NRSMat<double> a(n);
NRVec<double> rr(n);
for(int i=0;i<n;++i) for(int j=0;j<=i;++j)
{
a(i,j)= RANDDOUBLE();
if(i==j) a(i,i)+= .5*(i-n*.5);
}
NRSMat<double> aa;
NRMat<double> vv(n,n);
aa=a; diagonalize(aa,rr,&vv);
NRVec<double> r(m);
NRVec<double> *eivecs = new NRVec<double>[m];
double target= 0;
cout <<"Exact energies " <<rr<<endl;
davidson(a,r,eivecs,NULL,m,1,1e-6,1,200,300,(void (*)(LA::NRVec<double>&))NULL,&target);
cout <<"Davidson energies " <<r;
}
}//main