RW Wilson
uf - execute a user function which runs as a separate program,
     but has access to stack 1 from comb.


uf "userpg"		Execute the program 'userpg' with access to stack 1.


The named program is executed with two pipes set up.  The fd's of the
pipes are passed to the program as argument 1 and 2.  Stack 1 is sent
to the program over pipe 1 and it is read back from the program through
pipe 2.

The directory $COMB/src/user contains two programs userpg.c and ftnuser.c
and a subroutine ftnsub.f.  These programs take care of all of the
communication with comb.  I suggest that users copy these sources into 
new files for each application and put the instructions for making them 
in the makefile.  If several users want to use this facility, 
the best procedure is for each to copy these sources and 
the .h file(s) into his or her own directory and code specific 
applications there.

C users: userpg.c has a place to insert your code or 
         a call to your c subroutine.  Your subroutine should
         always write the process results back onto stack 1. (see

FORTRAN users: ftnuser.c has a call to ftnsub to do the work.  
               You can change the name of this subroutine by
	       editting ftnuser.c. ftnuser.c writes the process 
	       results back onto stack 1 whether you like it or not!

As an example, userpg is currently written to set the first channel 
of stack 1 to 37 and write the result back onto stack 1.  
To see this, (cd to $COMB/src/user) and execute:

-> p .stak1(1);uf "userpg";p .stak1(1)

Similarly, the FORTRAN routine ftnuser sets channel 2 to -37.  

-> p .stak1(2);uf "ftnuser";p .stak1(2)

(Actually .stak, .stak1, .stak(1), .stak1(1) all reference the 
 first channel of stack1.)

Comb will look in your path for the named program, or you can state
the full path explicitly.

Since a stack has room for 2048 channels, the user function can communicate
additional information back to comb in pre-arranged end channels.

This document was last updated on Tue Oct 17 16:24:05 EDT 2000 by Marc W. Pound.