Hi Michael,
I believe you can specify the initial guess without specifying the preconditioner. In place of the preconditioner, just pass '[]'. For example,
n = 100;
on = ones(n,1);
A = spdiags([-2*on 4*on -on],-1:1,n,n);
b = sum(A,2);
tol = 1e-8;
maxit = 15;
x0=zeros([n 1]);
x = bicg(A,b,tol,maxit,[],[],x0);
NOTE: The above example is just to let you know that it is syntactically possible to pass the initial guess to the function "bicg" without the preconditioner. The initial guess that I have used above is purely random and does not have a correlation with the underlying mathematics.
I hope this answers your question.
Regards,
Vidya
