AIPS HELP file for FOR in 31DEC20
As of Sat Feb 22 15:30:42 2020
Use: To establish an iterative loop, similiar to DO loops in FORTRAN
or PL/I. This construction may be used in procedures or in
immediate execution mode. In immediate mode, all statements
must be on the same line.
Grammar: FOR variable = start TO fini BY increment
statement1; statement2;... ; END
where 'variable' is a scalar variable that will change each
time through the loop, beginning at 'start', have 'increment'
added to it each time through the loop (the increment may be
positive or negative) and will end when the next loop would be
executed with 'variable' greater than (increment > 0; less than
with increment < 0) 'fini'. Note that the loop will be
executed at least once no matter what the start, fini and
increment parameters are. If the BY section is omitted, the
increment will default to 1.
Statementi are AIPS statements. These statements may not
have an omittted optional immediate numeric argument. Such
statements depend on the POPS stack being empty in the absence
of the argument. But the FOR loop uses the stack for the
'fini' and 'increment' values and so the stack is not empty.
Thus TVON with no argument will see a non-empty stack and
assume that it is getting an immediate argument from the stack.
Use in this case TVON(2**(TVCHAN-1)) inside your loop.
Verbs of this sort include EHEX, GROFF, GRON, HUEWEDGE,
IMWEDGE, REHEX, TVOFF, TVON, TVWEDGE.
Examples: FOR I = 1 TO 10; SUM = SUM + A(I); END
FOR I = K+3 TO K BY -1; A(I+1) = A(I); END
In the first example SUM will be incremented by the sum
of the first 10 elements in array A. The second example
will shift the section of array A between A(K) and A(K+3)
forward 1 element.