pentas.m

等高线拟合源代码（matlab源码）

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