gistfile1.matlab

function [d,V] = det_Krylov_preconditioned(A,P,precomputed, tol,maxiter)
n = length(A);
 V = probe(precomputed.colouring);
 
d= 0.0;
parfor iii=1:size(V,2)
    workerNo = get(getCurrentTask,'ID');
    fprintf('det_Krylov_preconditioned %d/%d\n', iii, size(V,2));
     [tmp,iter]=ratKrylov01_preconditioned(A,V(:,iii),P,precomputed.wsq,precomputed.dzdt,precomputed.const,tol,maxiter);
    d = d + V(:,iii)'*tmp;
end

gistfile2.matlab

function [b,iter] = ratKrylov01_preconditioned(A, z,P,wsq,dzdt,const,tol,maxiter)
 
N=length(dzdt);
dim=length(z);
 
b=zeros(dim,1);
b0=zeros(dim,1);
I=speye(size(A));
iter=0;
for jjj=1:N
 
    % CG is done on matrix M=A-wsq(jjj)*I, where A is the preconditioned term
    % Construct function M*x where Ax=P^(-1)*A*P^(-T)*x
    Ax_func=@(x) P\(A*((P')\x))   -wsq(jjj)*I*x;
    [b0,~,~,miter]=bicgstab(Ax_func,z,tol,maxiter,[],[],b0);
 
    b=b-dzdt(jjj)*b0;
    iter=iter+miter;
end
% b=const*A*imag(b);
b=const*(P\(A*((P')\imag(b))));