Dear Yunfei,
I think an article like this is what you need to get started:
https://www.sciencedirect.com/science/article/pii/S0045782521001468

Best regards
Bruno


On Thursday, August 28, 2025 at 3:23:28 p.m. UTC+2 [email protected] 
wrote:

> Dear Bruno,
>
> Thanks a lot for your reply. 
>
> I am not so clear on this part. I would be grateful if you could share 
> some documentation or an example to help me learn more about it.
>
> Best regards,
>
> Yunfei 
>
> [email protected] <[email protected]> 于2025年8月26日周二 15:11写道:
>
>> Dear Yunfei,
>> The linear system you solve depends on the weak form of the problem you 
>> are solving, which is established from the strong form of the PDE.
>> If you want to reconstruct the force from the displacement field, I think 
>> you would need to formulate the adjoint PDE problem to your displacement 
>> PDE. I think since the linear elasticity equation is a Poisson-ish 
>> equation, the equation would be self-adjoint and the adjoint system could 
>> be formed straightforwardly from the forward problem.
>>
>> I hope that helps
>> Bruno
>>
>> On Tuesday, August 26, 2025 at 1:31:04 p.m. UTC+2 [email protected] 
>> wrote:
>>
>>> Hi Everyone, 
>>>
>>> Now I have an inverse problem that is given the measured displacement 
>>> u_i and our target to get the force field f_j.  If I unstand correctly that 
>>> the linear system of dealii is A_{ij}u_j = f_i.   I am not sure this form 
>>> whether I can use the L2 regularization argmin{||u-u_{measure}|| + 
>>> \lamda||f|| }.  I have only had experience with A_(ij)f_j = u_i.  Then we 
>>> have an analytical solution using SVD. However,  If we have  A_{ij}u_j = 
>>> f_i, it looks like we do not have analytical solution.
>>>
>>> Does anyone have any ideas on how to solve this inverse problem using 
>>> dealii?
>>>
>>> Best regards, 
>>>
>>> Yunfei 
>>>
>>>
>>> -- 
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