demo3_vmg.m

五点差分型多重网格方法：各种插值算子的比较）

%==============================================
% Multigrid V-Cycle Solver, adapted for Demo 3.
%==============================================
% In this subrotinue ,I want to compute pdeerror and 
% average convergence factors over nine V-cycles on my model problem
% zhiyongfinish 2008
% Department of Computer Science
% University of xiangtan in China 

function [pde_error]=demo3_vmg(A,b,x,xtrue,rtol,prtol,max_it,max_time,max_mflop)

r0 = b - A * x;    r = r0;
rn0 = norm(r0);    rn = rn0;

iter = 0;    
i=2;
everyerror= [norm(r0)];
tic
while (rn > rtol * rn0 & iter < max_it)
    level = 1;
    [x,u1] = vmg_cycle(level,b,x);
    r = b - A*x;
    rn = norm(r); 
    iter = iter + 1;
    %results=update_results(results,'VMG',iter,rn);
    %pde_error = [pde_error; max(abs((xtrue-x)))];
    everyerror= [everyerror; norm(r)];
    f(i-1)=10^((log10(everyerror(i)/everyerror(1)))/(i-1));
    i=i+1;
end  
time=toc;
pde_error=max(abs((xtrue-x)));
factor_average=(f(1)+f(2)+f(3)+f(4)+f(5)+f(6))/6;
factor_one=10^(log10(everyerror(10)/everyerror(2))/9);
fprintf('%g, time spends=%g，factor_one=%g,factor_average=%g\n',pde_error,time,factor_one,factor_average); 
fprintf('error in starting = %g\n',max(abs(x-u1)));