[Trilinos-Users] GMRES faster than CG

Rony Speck speckro at hotmail.com
Thu Jun 19 03:50:27 MDT 2008

Hello everybody

When using AztecOO, I noticed that GMRES converges faster and needs less time than CG when using IFPACK IC or ML as a preconditioner. 
The difference is quite large. The system is spd. When using no preconditioner, CG needs less iterations and is faster.
I also plotted the iteration numbers against the norms of the residuals. For GMRES the curve is smooth, whereas for
CG the curve is rather erratic. For both solvers I set the convergence criterium to AZ_rhs. 

Has anyone else experienced this?

Thanks for your answers
Rony Speck

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