How to access discretized equations?

Hi folks, I want to use calculix to create a FEM discretization of a mechanical deformation model. The manual is a handful and doesn’t seem to say anything about how I can get the discretized equations. Does someone here know how to do this?

You can only write the matrices. Fortunately, CalculiX is open-source so you could examine the source code and see how it solves problems internally. There’s also Guido Dhondt’s book that serves as a theory manual for CalculiX.

How exactly can I get the matrices? And is the book you’re talking about the “CalculiX CrunchiX User’s Manual”?

Matrices are written using *FREQUENCY, SOLVER=MATRIXSTORAGE (possible with *BUCKLE and *HEAT TRANSFER too).

User’s Manual is just a documentation with not so much theoretical background. But Guido Dhondt (CalculiX developer) wrote a book that can be treated as a theory guide for CalculiX: “The Finite Element Method for Three‐Dimensional Thermomechanical Applications”.

Thank you so much! I’ll take a look at those. If I have to dive into the source code I hope it’s not too difficult to get started with modifying it.

It can be rather difficult to get familiar with because there aren’t many comments and the structure is quite specific. Also, it’s written mostly in Fortran.

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Alright, thanks for the heads up. I’ll try to avoid that.

Also, try to start with a simple problem. Something that you can actually calculate by hand and check the output of the code. As mentioned by @Calc_em , it is pretty challenging to dive into the source code with the minimum comments on the subroutines, etc.

Yeah that was my plan, jumping into the deep end straight away is gonna make things way too complex. Are there any experts on here who might be able to talk me through a piece of Calculix code if I ever run into any trouble?