Access and modify Global stiffness matrix

[nima_ikm]

Hello,

I need to do static condensation of my stiffness matrix and residual, as well. What I mean I need to just retain d.o.f for interface and condensed out other d.o.f. Based on this I have following questions:

1. My aim is to write umacr after “TANG” to do static condensation and transfer the condensed stiffness to text file. I want to know where is the global stiffness stored. I mean what is the allocation number hr(np(...)). For example, how 'OUTPUT' command compute 'TANG' (from which sparse array).

2. Is it possible to change global stiffness to condensed matrix and use 'SOLVE' command. (by just active corresponding d.o.f and deactivate others) Or I should solve condensed stiffness in another external FORTRAN program like lapack.

3.I want to add another stiffness matrix (A) to my global stiffeners (K) before solving system of equation. What I mean, I need to solve : (A+K)U=F. I would like to know what is your suggestion for this problem Maybe I can write one umacr after (TANG) and modified global stiffness matrix before going to SOLVE command.
P.S. Matrix, A (additional stiffness), is stored in one text file which can be read through umacr.

I would be appreciate if you could have any other idea to do static condensation.

Thank you so much for your kind help, in advance.

Best regards

[Prof. R.L. Taylor]

The attached file does an input of a matrix in I J A(I,J) form and adds to the stiffness matrix.

It has not been used much but may help you see what you can implement.

The reduction of the stiff and adding in the matrix is not fully supported.  There is a fragment of an EXPOrt and IMPOrt command in feap that is intended to help with this but is not active -- you need to study and add what you need.

[nima_ikm]

Dear Professor Taylor,

Thank you very much for your kind information and files. I am so appreciated.

Thanks a lot