Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!batcomputer!riley
From: riley@batcomputer.tn.cornell.edu (Daniel S. Riley)
Newsgroups: comp.lang.fortran
Subject: Re: fortran statement
Message-ID: <8531@batcomputer.tn.cornell.edu>
Date: 31 Jul 89 13:51:59 GMT
References: <28605@beta.lanl.gov> <588BLUMBERG@BGUVM> <10632@smoke.BRL.MIL>
Reply-To: riley@tcgould.tn.cornell.edu (Daniel S. Riley)
Organization: Cornell Theory Center, Cornell University, Ithaca NY
Lines: 30

In article <10632@smoke.BRL.MIL> chidsey@brl.arpa (Irving Chidsey (INF) <chidsey>) writes:
>In article <588BLUMBERG@BGUVM> BLUMBERG@BGUVM.BITNET (Dan Blumberg, Dept. Of Geog. Ben Gurion Univ. Israel) writes:
><mod is the name of a two fimensional matrix sized I by J. MOd (n,2) is the
><cell in matrix Mod with the coordinates of n,2(like geographical coordinates).

>Sorry, but mod( n, 2 ) is almost certainly Fortran for N modulo 2, which is
>mathematics for n/2 with no fractional part.
>
>I don't thinkit is standard fortran, but it is common fortran.

Ok, enough of this.

mod() is the remainder function.  mod(n, 2) returns the remainder when
n is divided by 2--this is the usual way to check for even or odd (or test 
the least significant bit, same thing).  It is a standard FORTRAN-77 
intrinsic.  The definition is something like

mod(n, m) = n - m*int(n/m)

mod() is really misnamed, since it returns the remainder, not the modulo.
(For those who care--the remainder takes the sign of the first argument,
the modulo takes the sign of the second.  mod(x, 2*pi) ought to return a
number between 0 and 2*pi, but in FORTRAN-77 it returns a number between
-2*pi and 2*pi, depending on the sign of x.)

As far as I know, you could declare an array named mod(), but this is
generally considered to be bad (and confusing) programming practice.

-Dan Riley (riley@tcgould.tn.cornell.edu, cornell!batcomputer!riley)
-Wilson Lab, Cornell U.