## hb_write -- Write a sparse matrix to a file in the Harwell-Boeing 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`.
b
  Rigth hand side.
  Type: Optional
  An array of type real or complex, rank 1 and having the ALLOCATABLE attribute; will be allocated and filled in if the input file contains a right hand side.
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 `-`.
key
  Matrix key.
  Type: Optional
  A charachter variable of length 8 holding the matrix key as specified by the Harwell-Boeing format and to be written to file.
mtitle
  Matrix title.
  Type: Optional
  A charachter variable of length 72 holding the matrix title as specified by the Harwell-Boeing format and to be written to file.

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