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Re: [Getfem-users] Generic Bricks definition using gf_asm.


From: Nicolò Cambiaso
Subject: Re: [Getfem-users] Generic Bricks definition using gf_asm.
Date: Wed, 2 Oct 2019 15:58:16 +0200

I'm sorry to bother you again, but a couple of questions raised.

Some of the blocks are symmetric, so in my matrix i'll have the transposed corresponding block. Do I need to create the transposed block too with the command gf_asm('generic' ...) or it's going to do it by himself?

Also,
From the equation, I have a term comprendig a test function and some static initial data defined in the whole mesh, but no variables ('A*test_pv'). This term is gonig to be in the Right Hand Side of the linear system. Now, my question is: which one of the functions (gf_asm('function', ...)) is the correct one to use? Is again 'generic' going to understand it? Right now i bet on  'volumic source', but i defined nowhere which test function i'm using, so i'm not so sure about that.

Thank you for your help and your time.
Have a nice day,
Nicolò Cambiaso

Il giorno mer 2 ott 2019 alle ore 09:37 Nicolò Cambiaso <address@hidden> ha scritto:
Thank you very much, now it works.
to completeness to the future readers, I would like to correct a typo I made when asking for the command.
K= --equation--
gf_model_set(md, 'add initialized data', 'K', [K]);
gf_asm('generic', mim3, 2, 'K*(Test_ut.*ut)', -1, 'ut', 1, mf3, zeros(gf_mesh_fem_get(mf3, 'nbdof'),1), 'K' , 0, K);

Again, thank you,
Have a nice day
Nicolò Cambiaso

Il giorno lun 30 set 2019 alle ore 22:19 Yves Renard <address@hidden> ha scritto:

Dear Nicolo Cambiaso,

You can use gf_asm to produce a mass matrix as you tried, but you have to specify a fem on which the variable is described. The correct syntax is for instance

gf_asm('generic', mim3, 2, 'Grad_Test2_ut.Grad_Test_ut', -1, 'ut',1, mf, zero(gf_mesh_fem_get(mf, 'nbdof'),1));

where mf is the mesh_fem structure describing the fem.

Best regards,

Y.R.

----- Mail original -----
De: "Nicolò Cambiaso" <address@hidden>
À: "getfem-users" <address@hidden>
Envoyé: Lundi 30 Septembre 2019 12:25:51
Objet: [Getfem-users] Generic Bricks definition using gf_asm.

Dear users,
I would like to solve a system of equations using Getfemm++ with Matlab
interface.
So I created a block matrix, and now i cannot create the corresponding
bricks.
I'm using the command "gf_asm", hoping it's the correct one.

the block is the following:
Mtt=1/k u_t v_t. (v_t is the test function corresponding to u_t)
in full despair, i also removed the 1/k therm, and still nothing worked.
this is what i wrote:

gf_asm('generic', mim3, 2, 'Grad_Test2_ut.Grad_Test_ut', -1, 'ut',1, U);

And the error message is:

"Error using gf_matlab
Error in getfem_generic_assembly.cc, line 9519 void
getfem::ga_node_analysis(const string&, getfem::ga_tree&, const
getfem::ga_workspace&, getfem::pga_tree_node, bgeot::size_type,
bgeot::size_type, bool, bool, int):
Error in assembly string

Error in gf_asm (line 338)
    [varargout{1:nargout}]=gf_matlab('asm', varargin{:});

Error in Comeon (line 56)
Mtt=gf_asm('generic', mim3, 2, 'Grad_Test2_ut.Grad_Test_ut', -1, 'ut',1,
U);  % M_tt, proviamo"

with
mim3= gf_mesh_im( mf3, gf_integ('IM_NC(3,1)') )
mf3=gf_mesh_fem(OmegaM,3)
OmegaM=gf_mesh('regular simplices',vectX, vectY, vectZ, 'degree', 1)

at his point, i defined U as ones(2,2,2,3), having the vectX(/Y/Z) only 2
points each one, for now, and because u_t is a 3D vector.
I think that's not correct, but i have no idea of the correct dimension of
U, and i tried everything that came to my mind ... and still nothing
worked.

I found a lot of material dealing with this on c++ interface, but
unfortunately I cannot male it work in Matlab.

thank you very much,
Nicolo Cambiaso.

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