stmm routines multiply a symmetric banded Toeplitz matrix by the data matrix. The Toeplitz matrix size is assumed to be equal to that of the data matrix. If this is not the case use stbmm routines instead. If the data matrix is distributed over multiple processes the Toeplitz matrix has to be defined on each of them and has to be the same on each of them, including the first and the last row indices used to defined its region.