Re: [Getfem-users] Divergence of the first Piola-Kirchhoff stress tensor

[Yves Renard]

Dear Phuoc,

I think the correct expression with Contract is simply

div_sigma = "(Contract(Grad(first_Piola_Kirchhoff_stress), 2, 3))"

Contract makes a summation with respect to the given indices, so that 
Contract(A, 2, 3) = A_{i,j,j} with summation on j.

Can your try again with the fix I commited to the master branch ?

Best regards,

Yves



----- Original Message -----
From: "Huu Phuoc BUI" <address@hidden>
To: "yves renard" <address@hidden>
Cc: "franz chouly" <address@hidden>
Sent: Friday, 13 July, 2018 12:00:55
Subject: Re: [Getfem-users] Divergence of the first Piola-Kirchhoff stress 
tensor

Dear Yves,

Thank you very much for your email.

Please find enclosed a minimal code.

I am not sure that I use correctly the Contract operator, you will find 
therefore both the original code and the new one for div_sigma:

/div_sigma = "[Contract(Grad(first_Piola_Kirchhoff_stress)(1,:,:),1,2), 
Contract(Grad(first_Piola_Kirchhoff_stress)(2,:,:),1,2), 
Contract(Grad(first_Piola_Kirchhoff_stress)(3,:,:),1,2)].[1,1,1]"/

Please let me know if you find the problem. Thank you!

Best regards,
Phuoc

On 13/07/2018 08:59, Yves Renard wrote:
>
> Dear Phuoc,
>
> No, a priori this should work. To simplify a bit your expression, you 
> can use Contract(Grad(...), 2, 3).[1,1,1] instead of the three traces 
> in div_sigma.
>
> If you give me a minimal code, I could have a look to the problem.
>
> Best regards,
>
> Yves
>
>
> Le 12/07/2018 à 15:36, Huu Phuoc BUI a écrit :
>>
>> Dear GetFEM-users,
>>
>> As Grad(expression) is available in the new version of GetFEM++, I 
>> compute the divergence of the first Piola-Kirchhoff stress tensor as 
>> (python code):
>>
>> /div_sigma = "( Trace(Grad(first_Piola_Kirchhoff_stress)(1,:,:)) + 
>> Trace(Grad(first_Piola_Kirchhoff_stress)(2,:,:)) + 
>> Trace(Grad(first_Piola_Kirchhoff_stress)(3,:,:)) )"/
>>
>> in which first_Piola_Kirchhoff_stress is a macro of a model /md/, 
>> which is defined as:
>>
>> /md.add_macro("second_Piola_Kirchhoff_stress", 
>> "Compressible_Mooney_Rivlin_sigma(Grad_u, [c1;c2;d1])")//
>> //md.add_macro("first_Piola_Kirchhoff_stress", 
>> "(Id(meshdim)+Grad_u)*second_Piola_Kirchhoff_stress")/
>>
>> Then I use generic assembly to assembly this quantity as:
>>
>> /eta_L_1_tmp = gf.asm_generic(mim,1,"(("+div_sigma+").delta)*Test_t",-1//
>> //                             ,md//
>> //                             ,"delta", False, mfz, delta//
>> //                             ,"t", True,mfrj,np.zeros(mfrj.nbdof()) )/
>>
>> with /delta/ a given vector on a meshfem /mfz/.
>>
>> When executing the code, GetFEM++ only gives the error as
>>
>> /segmentation fault (core dumped)/
>>
>> If you see any problem in my code, please let me know. Thank you in 
>> advance.
>>
>> Best regards,
>>
>> Phuoc
>>
>>
>
> -- 
>
>    Yves Renard (address@hidden)       tel : (33) 04.72.43.87.08
>    Pole de Mathematiques, INSA-Lyon             fax : (33) 04.72.43.85.29
>    20, rue Albert Einstein
>    69621 Villeurbanne Cedex, FRANCE
>    http://math.univ-lyon1.fr/~renard
>
> ---------