Interface routines

                     +------------------------------+
                     |CALL  IZFILE (LUN,CHDIR,CHOPT) |
                     +------------------------------+
Action: This routine declares a pre-open direct acces file to be ZEBRA/RZ file. Parameter Description:
LUN
Logical unit number.
CHDIR
CHARACTER variable specifying the name of the top directory.
CHOPT
CHARACTER variable specifying the option(s) desired:
'N'
Creates a New RZ file with top directory name CHDIR
' '
Open an existing RZ file with read only access.
'U'
Open an existing RZ file in Update mode.
'A'
Pictures are Automatically saved on disk.
When option 'A' is given or when option AURZ is activated by IGSET, pictures are automatically saved into the RZ file. In this case, there is only one picture in memory (the current picture). The last current picture is written on disk when IGEND is called. 
          +----------------------------------------------------+
          |CALL  IZOPEN (LUN,CHDIR,CFNAME,CHOPT,*LRECL*,ISTAT*) |
          +----------------------------------------------------+
Action: Open a HIGZ/RZ picture file. This routine open a direct access file and call IZFILE. Parameter Description:
LUN
Logical unit number.
CHDIR
CHARACTER variable specifying the name of the top directory.
CFNAME
File name.
CHOPT
CHARACTER variable specifying the option(s) desired:
'N'
Creates a New RZ file with top directory name CHDIR
' '
Open an existing RZ file with read only access.
'U'
Open an existing RZ file in Update mode.
'A'
Pictures are Automatically saved on disk.
LRECL
Integer variable specifying the record length of the file in machine words. If a value of zero (0) is specified IZOPEN will attempt to obtain the correct record length from the file itself. A value of zero must not be specified for new files.
ISTAT
Integer variable in which the status code is returned.
When option 'A' is given or when option AURZ is activated by IGSET, pictures are automatically saved into the RZ file. In this case, there is only one picture in memory (the current picture). The last current picture is written on disk when IGEND is called. 
                       +--------------------------+
                       | CALL  IZIN (PNAME,ICYCLE) |
                       +--------------------------+
Action: This routine reads a picture from an RZ data file and puts it in memory. Parameter Description:
PNAME
CHARACTER variable specifying the name of picture to be read.
ICYCLE
Cycle number of the picture to be read. If ICYCLE is greater than the highest existing cycle number on the RZ file, then the picture with the highest cycle number is read. 
                      +----------------------------+
                      | CALL  IZOUT (PNAME,ICYCLE*) |
                      +----------------------------+
Action: This routine writes on an RZ data file a memory resident picture. Parameter Description:
PNAME
CHARACTER variable specifying the name of picture to be written.
ICYCLE*
Cycle number of the picture written. If a picture with name PNAME does not already exist on the output file, then a value for ICYCLE of 1 is returned, otherwise a value one higher than the (previous) highest cycle number on the file. 

                       +--------------------------+
                       |CALL  IZSCR (PNAME,ICYCLE) |
                       +--------------------------+
Action: This routine deletes (scratches) a picture from an RZ data file. Parameter Description:
PNAME
CHARACTER variable specifying the name of picture to be deleted.
ICYCLE
Cycle number of the picture to be deleted.