AIPS HELP file for BY in 31DEC13
As of Sat May 18 6:41:50 2013
Use: In the FOR loop construction BY is used to signal the
value by which to increment the incrementing variable.
(See HELP FOR). This value may be negative. The
inclusion of BY is optional. If omitted, the increment
will default to 1.
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
Example: FOR I = K+3 TO K BY -1; A(I+1) = A(I); END
This example will shift the section of array A between
A(K) and A(K+3) forward 1 element.