Introduction to Computational Linear Algebra

192 Introduction to Computational Linear Algebra

nnz gives the number of non-zero coefficients. Algorithm 7.5 generates

the non-zero coefficients of A.

Algorithm 7.5 Sparse Finite Difference Two-Dimensional Poisson Matrix

function [I,J,s,IB,UNK,f,U]=coeffa(pih,pik)

% UNK is the set of indices corresponding to the unknowns

% IB is the set of border indices

% J in IB: there exists an interior node such that s(I,J)~=0

% Pt is the coeffa table pointer. It is initialized to 0

UNK=[];IB=[];Pt=0;m=length(pih);n=length(pik);

[xs,ys,is,js,id,a,f,U]= Nodes(pih,pik);

%Computing the vector H={hi, i=1, ...,m-1}

% and K={kj, j=1, ...,n-1}

H=diff(pih);h=max(pih);K=diff(pik);h=max(pik); ...