GMRES same iterations number

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María José Castellano
回答： Steven Lord 2018-8-28
Hi, I'm solving three linear systems with GMRES for a numerical problem for Helmholtz equation using 3 different meshes but my problem is even if the matrix gets big and its conditioning gets lower the GMRES function gives me the same number of iterations. I use the command [q,flag,relres,iter,resvec] = gmres(Sq,uinc,10,[],100); Thanks for the answers

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Steven Lord
Steven Lord 2018-8-28
You told gmres to use a maximum of 100 outer iterations. Are all your calls to gmres reporting that they took 100 iterations (the first element of the output variable iter is equal to 100?) If so, check your convergence flag output (the variable named flag in your call.) My guess is it will be 1, indicating "gmres iterated maxit times but did not converge."

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