Re: [Getfem-users] Re-assemble one brick in a model

[Yves Renard]

Dear Magnus,

Getfem model terms are not re-assembled if you make multiple solves and if the 
data they depend on do not change.

So, in you case, you can perform between two solve a

md.set_variable('WF', NewWF) 

Where NewWF is your new vector of values for the data WF.
Then the Helmholtz brick will not be re-assembled. Only the right hand side 
will be.

However, of course, the linear system will be solved at each solve. There is no 
option for the moment to perform say a LU decomposition only once and apply 
several second hand. If you ant to perform this, you have to mak a specific 
solve by yourself (you can extract the assembled matrix and righ hand side).


Best regards,

Yves.




----- Mail original -----
De: "Magnus Paulsson" <address@hidden>
À: "getfem-users" <address@hidden>
Envoyé: Vendredi 18 Décembre 2015 16:56:46
Objet: [Getfem-users] Re-assemble one brick in a model

I’m using the python interface to solve a Helmholtz problem and want to repeat 
the solution for many different values of the Dirichlet boundary conditions. 
The question is: Can I use the model framework and only re-assemble the part 
that I want to change without assembling the full problem? 
(Or do I have to assemble the parts myself ...) 

As I do it today I repeat the following where the “mfWF” variable is updated 
and assembles the full problem for each value of the boundary conditions: 

################################################ 
import numpy as N 

md = GF.Model('complex') 

# Helmholtz brick 
md.add_fem_variable('psi', mf) 
md.add_initialized_fem_data('sqrtpot', mf, N.sqrt(-mfPot.astype(N.complex))) 
md.add_Helmholtz_brick(mim,'psi','sqrtpot') 
# Zero boundary 
md.add_initialized_data('zerov', 0) 
md.add_Dirichlet_condition_with_multipliers(mim,'psi',mf,[zeroSide],'zerov') 

# Wavefunction boundary 
md.add_initialized_fem_data('WF', mf, mfWF) 
md.add_Dirichlet_condition_with_multipliers(mim, 'psi', mf, [wfSide], 'WF') 

# Periodic boundary conditions 
numPBC = pbcMat.size()[0] 
md.add_variable('mult', numPBC) 
md.add_constraint_with_multipliers('psi', 'mult', pbcMat, 
N.zeros(numPBC,N.complex)) 

md.solve() 
################################################ 

What I would like to do is to replace the md.solve() line with: 
for ii in mfWFs: 
md.add_initialized_fem_data('WF', mf, ii) 
md.solve() 

Is this possible (from the documentation I kind of guess that the 
enable_bricks, disable_bricks etc are there for this kind of purpose but it’s 
not clear). 
Finally, thank you for the GetFEM software. Awesome. 

----------------------------------------------- 
Magnus Paulsson 
Associate Professor 
Dept. of Physics and Electrical Engineering 
Linnaeus University 
Phone: +46-480-446308 
Mobile: +46-70-6942987 



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