## hb_read -- Read a sparse matrix from a file in the Harwell-Boeing format

Type:
  Asynchronous.
On Entry
filename
  The name of the file to be read.
  Type:optional.
  Specified as: a character variable containing a valid file name, or `-`, in which case the default input unit 5 (i.e. standard input 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
a
  the sparse matrix read from file.
  Type:required.
  Specified as: a structured data of type spdata`psb_Tspmat_type`.
b
  Rigth hand side(s).
  Type: Optional
  An array of type real or complex, rank 2 and having the ALLOCATABLE attribute; will be allocated and filled in if the input file contains a right hand side, otherwise will be left in the UNALLOCATED state.
mtitle
  Matrix title.
  Type: Optional
  A charachter variable of length 72 holding a copy of the matrix title as specified by the Harwell-Boeing format and contained in the input file.
iret
  Error code.
  Type: required
  An integer value; 0 means no error has been detected.