Arash Zamani's blog

Dear All,I have written a finite element code in C++. The results have generally high accuracy. But when I change the order of evaluating r and theta of the polar coordinates in terms of x and y in the sub-program of computing the shape functions, then the results are changed about 10^-9 of the initial results. The change is negligible but I wonder why this happens? I had initially supposed it may be related to some memory linkage in the program but since now I have not been successful to find any. Is there any one to have an idea about this funny error???

Dear All,

I have written a finite element code in C++. The results have generally high accuracy. But when I change the order of evaluating r and theta of the polar coordinates in terms of x and y in the sub-program of computing the shape functions, then the results are changed about 10^-9 of the initial results. The change is negligible but I wonder why this happens? I had initially supposed it may be related to some memory linkage in the program but since now I have not been successful to find any. Is there any one to have an idea about this funny error???

In the FEM book by KJ Bathe and also in the fem book by G.Dhatt, it is said the direct solvers are generally more convenient than iterative solvers and new versions of them include reordering and efficient use of skyline method. In contrast there are iterative solvers with capability to directly manipulate sparse format of matrices. I am now working on XFEM coding with C++ and don't know what type of solver would be the best for XFEM. the conditioning issues of matrices obtained from XFEM would be a difficulty for the choice of preconditioners.