function [f_result,p_flag]=pentas(n,a,b,c,f)%[f_result,p_flag]=pentas(n,a,b,c,f)% To solve symmetric 5-diagonal lineair system of equations% a is diagonal (1...n), is overwritten% b is first subdiagonal 1...n-1 , is overwritten% c is second subdiagonal 1...n-2, is overwritten% f is right-hand side input% f_result solution vector.% dimensions of a,b,c,f are n% return p_flag = 0  ok,   %               = 2  The matrix is numerical singular  p_flag = 0; h1=0; h2=0; h3=0; h4=0; h5=0; hh1=0; hh2=0; hh3=0; hh4=0; hh5=0; for k=1:n,  z=a(k)-h4*h1-hh5*hh2;  if abs(z)<eps,    p_flag=2;    return;  end  hb=b(k);  hh1=h1;  h1=(hb-h4*h2)/z;  b(k)=h1;  hc=c(k);  hh2=h2;  h2=hc/z;  c(k)=h2;  a(k)=(f(k)-hh3*hh5-h3*h4)/z;  hh3=h3;  h3=a(k);  h4=hb-h5*hh1;  hh5=h5;  h5=hc; end h2=0.0; h1=a(n); f(n)=h1; for k=n-1:-1:1,     f(k)=a(k)-b(k)*h1-c(k)*h2;     h2=h1;     h1=f(k); end f_result=f; return