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svd_solve optionally report nullity

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Jiri Pittner
2026-02-11 18:03:21 +01:00
parent f8923b1a3f
commit 1735b35909
1 changed files with 14 additions and 4 deletions
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18
nonclass.h
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@@ -169,29 +169,39 @@ declare_la(std::complex<double>)
//svd_solve without contamination from nullspace, b is n x nrhs, result returns in b, A is destroyed
template<typename T>
NRVec<T> svd_solve(NRMat<T> &a, const NRVec<T> &b, double thres=1e-12)
NRVec<T> svd_solve(NRMat<T> &a, const NRVec<T> &b, double thres=1e-12, int *nullity = NULL)
{
if(b.size()!=a.nrows()) laerror("size mismatch in svd_solve");
if(nullity) *nullity=0;
NRVec<double> w(a.ncols());
NRMat<T> u(a.nrows(),a.ncols());
NRMat<T> vt(a.ncols(),a.ncols());
singular_decomposition(a,&u,w,&vt,false);
NRVec<T> utb = b*u;
for(int i=0; i<w.size(); ++i) utb[i] = w[i]>thres ? utb[i]/w[i] : 0.;
for(int i=0; i<w.size(); ++i)
{
if(w[i]>thres) utb[i] /= w[i];
else {utb[i]=0; if(nullity) ++*nullity;}
}
return utb*vt;
}
template<typename T>
NRMat<T> svd_solve(NRMat<T> &a, const NRMat<T> &b, double thres=1e-12)
NRMat<T> svd_solve(NRMat<T> &a, const NRMat<T> &b, double thres=1e-12, int *nullity = NULL)
{
if(b.nrows()!=a.nrows()) laerror("size mismatch in svd_solve");
if(nullity) *nullity=0;
NRVec<double> w(a.ncols());
NRMat<T> u(a.nrows(),a.ncols());
NRMat<T> vt(a.ncols(),a.ncols());
singular_decomposition(a,&u,w,&vt,false);
NRVec<T> ww(w.size());
for(int i=0; i<w.size(); ++i) ww[i] = w[i]>thres ? 1./w[i] : 0.;
for(int i=0; i<w.size(); ++i)
{
if(w[i]>thres) ww[i] = 1./w[i];
else {ww[i]=0; if(nullity) ++*nullity;}
}
NRMat<T> utb(a.ncols(),b.ncols());
utb.gemm((T)0,u,'c',b,'n',(T)1);
utb.diagmultl(ww);