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Re: [Getfem-users] gmres did not converge!

From: Konstantinos Poulios
Subject: Re: [Getfem-users] gmres did not converge!
Date: Thu, 2 May 2019 15:03:36 +0200

Dear Zhenghuai Guo,

Why don't you use a direct solver (MUMPS)? Direct solvers are much more robust, especially if your model contains Lagrange multipliers.


On Thu, May 2, 2019 at 2:57 PM Zhenghuai Guo <address@hidden> wrote:
Hi, Andriy and Yves and Konstantinos,

I loaded two meshes, totally about 350000 elements.

I only added elasticity bricks:
  getfem::add_isotropic_linearized_elasticity_brick(model, mim_1, "u_1", "lambda_1", "mu_1");
  getfem::add_isotropic_linearized_elasticity_brick(model, mim_2, "u_2", "lambda_2", "mu_2");

and four pointwise_constraints (two more each mesh):
  getfem::add_pointwise_constraints_with_multipliers(model,"u_1","point_1_1","point_1_1_unitx", "point_1_1_valuex");
  getfem::add_pointwise_constraints_with_multipliers(model,"u_1","point_1_1","point_1_1_unity", "point_1_1_valuey");
  getfem::add_pointwise_constraints_with_multipliers(model,"u_1","point_1_2","point_1_2_unitx", "point_1_2_valuex");
  getfem::add_pointwise_constraints_with_multipliers(model,"u_1","point_1_2","point_1_2_unity", "point_1_2_valuey");
  getfem::add_pointwise_constraints_with_multipliers(model,"u_2","point_2_1","point_2_1_unitx", "point_2_1_valuex");
  getfem::add_pointwise_constraints_with_multipliers(model,"u_2","point_2_1","point_2_1_unity", "point_2_1_valuey");
  getfem::add_pointwise_constraints_with_multipliers(model,"u_2","point_2_2","point_2_2_unitx", "point_2_2_valuex");
  getfem::add_pointwise_constraints_with_multipliers(model,"u_2","point_2_2","point_2_2_unity", "point_2_2_valuey");

 The values for the pointwise_constraints are simply the same as -1. This means the two meshes should just be translated parallelly by -1 in both x and y direction.

My solver is
  gmm::iteration iter(1E-9, 1, 100);
  getfem::standard_solve(model, iter);

But I get warning of not convergence:
iter   0 residual            1
 iter 500 residual  6.17288e-05
Level 2 Warning in getfem/getfem_model_solvers.h, line 127: gmres did not converge!

I am quite sure that my mesh looks good and have no strange shape elements. When I use small simply meshes, the code runs ok.
Could you please advise to me how to improve?

Zhenghuai Guo

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