can you use bicg with initial guess but without preconditioner. If so, how do you call it?

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Michael Stopa 2016-3-25

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评论： Michael Stopa 2016-3-30

采纳的回答： Vidya Viswanathan

can you use bicg with an initial guess, x0, but without specifying a preconditioner M or M1, M2?

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Answer 1

Vidya Viswanathan 2016-3-30

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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