Nastran can output results in many different formats: printed results in .f06 and punch files, binary results in output2, output4, xdb files, etc. To which results and which format are you referring?
Assuming you are talking about output2, the fomat of that file is documented in the https://docs.plm.automation.siemens.com/tdoc/nxnastran/11/help/#uid:index_dmap. See the Module Description for OUTPUT2 (which defines the general format of the file) and the Data Block descriptions for the specific results datablocks you are interested in.
thanks for the reply and I was talking about .OP2 file.
In this case, I suppose, I should look for OUTPUT2 description.
is OUTPUT4 much simpler ? It deals with only Matrices and should be sufficient for results.
It's hard to recommend any one format as you haven't specifically defined what you are trying to accomplish.
output4 is matrix oriented if you are simply trying to access a matrix.
There are utilities availablle that can read and write output4 from Matlab, for example.
The pyNastran project supports reading and writing BDF, F06, OP2 and OP4 via Python.