Retrieve the Cholesky factorization at the scilab level (original) (raw)

Scilab 5.3.3

• Scilab help
• UMFPACK Interface (sparse)
• PlotSparse
• ReadHBSparse
• cond2sp
• condestsp
• rafiter
• res_with_prec
• taucs_chdel
• taucs_chfact
• taucs_chget
• taucs_chinfo
• taucs_chsolve
• taucs_license
• umf_license
• umf_ludel
• umf_lufact
• umf_luget
• umf_luinfo
• umf_lusolve
• umfpack

Please note that the recommended version of Scilab is 2026.0.1. This page might be outdated.
See the recommended documentation of this function

Scilab help >> UMFPACK Interface (sparse) > taucs_chget

taucs_chget

retrieve the Cholesky factorization at the scilab level

Calling Sequence

[Ct,p] = taucs_chget(C_ptr)

Arguments

C_ptr

a pointer to the Cholesky factorization (C,p : A(p,p)=CC')

Ct

a scilab sparse matrix (you get the upper triangle i.e. Ct is equal to C')

p

column vector storing the permutation

Description

This function may be used if you want to plot the sparse pattern of the Cholesky factorization (or if you code something which use the factors). Traditionnaly, the factorization is written :

with P' the permutation matrix associated to the permutation p. As we get the upper triangle Ct (= C'), in scilab syntax we can write :

Examples

A = sparse( [ 2 -1 0 0 0; -1 2 -1 0 0; 0 -1 2 -1 0; 0 0 -1 2 -1; 0 0 0 -1 2] ); Cp = taucs_chfact(A); [Ct, p] = taucs_chget(Cp); full(A(p,p) - Ct'*Ct)
taucs_chdel(Cp)

stacksize(3000000)

[A] = ReadHBSparse(SCI+"/modules/umfpack/examples/bcsstk24.rsa");

Cptr = taucs_chfact(A);

[Ct, p] = taucs_chget(Cptr);

xset("window",0) ; clf() PlotSparse(A) ; xtitle("Initial matrix A (bcsstk24.rsa)")

B = A(p,p); xset("window",1) ; clf() PlotSparse(B) ; xtitle("Permuted matrix B = A(p,p)")

xset("window",2) ; clf() PlotSparse(Ct) ; xtitle("The pattern of Ct (A(p,p) = C*Ct)")

[OK, n, cnz] = taucs_chinfo(Cptr)

cnz_exact = nnz(Ct)

taucs_chdel(Cptr)

See Also

• taucs_chfact — cholesky factorisation of a sparse s.p.d. matrix
• taucs_chsolve — solve a linear sparse (s.p.d.) system given the Cholesky factors
• taucs_chdel — utility function used with taucs_chfact
• taucs_chinfo — get information on Cholesky factors
• taucs_chget — retrieve the Cholesky factorization at the scilab level
• cond2sp — computes an approximation of the 2-norm condition number of a s.p.d. sparse matrix

Authors

• taucs by Sivan Toledo (see taucs_license)
• scilab interface by Bruno Pincon