## mm_mat_write -- Write a sparse matrix to a file in the MatrixMarket format

Type:
  Asynchronous.
On Entry
a
  the sparse matrix to be written.
  Type:required.
  Specified as: a structured data of type spdata`psb_Tspmat_type`.
mtitle
  Matrix title.
  Type: required
  A charachter variable holding a descriptive title for the matrix to be written to file.
filename
  The name of the file to be written to.
  Type:optional.
  Specified as: a character variable containing a valid file name, or `-`, in which case the default output unit 6 (i.e. standard output in Unix jargon) is used. Default: `-`.
iunit
  The Fortran file unit number.
  Type:optional.
  Specified as: an integer value. Only meaningful if filename is not `-`.

On Return
iret
  Error code.
  Type: required
  An integer value; 0 means no error has been detected.