Hello Massochy,
Here is the code:
! below commands create dense matrix
! Stiffness
*DMAT, MatKD, D, IMPORT, FULL, file. full, STIFF
*PRINT, MatKD, Kdense.matrix
! Mass
*DMAT, MatMD, D, IMPORT, FULL, file. full, MASS
*PRINT, MatMD, Mdense.matrix
! below commands create sparse matrix
*SMAT, MatKS, D, IMPORT, FULL, file. full, STIFF
*PRINT, MatKS, Ksparse.matrix
! Mass
*SMAT, MatMS, D, IMPORT, FULL, file. full, MASS
*PRINT, MatMS, Msparse.matrix
Best,
Nanda