Re: function IF with several equality conditions
- To: mathgroup at smc.vnet.net
- Subject: [mg49111] Re: function IF with several equality conditions
- From: Bill Rowe <readnewsciv at earthlink.net>
- Date: Thu, 1 Jul 2004 05:26:16 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
On 6/30/04 at 5:34 AM, mbekkali at gmail.com (Mukhtar Bekkali) wrote:
>I have two questions that HELP file of Mathematica does not
>address:
>(1) How do I implement IF with several conditions. I tried
>something like this
>a=1; Table[If[{x1>a,x2<a},0,1],{x1,0,2},{x2,0,2}]
>and get no results.
The construct {expr1, expr2 ... } is a list of expressions and doesn't have a true/false value. Change the code to read
Table[If[x1>a && x2<a,0,1],{x1,0,2},{x2,0,2}]
or
Table[If[And@@{x1>a,x2<a},0,1],{x1,0,2},{x2,0,2}]
and you will get what you want
>Also, (2) IF does not accept equality conditions either, say
>a=1; Table[If[x=a,0,1],{x,0,2}]
The operator "=" is the assignment operator not a test for equality. You need to use "==" as in
Table[If[x==a,0,1],{x,0,2}]
>I am surprised that such simple things are not covered by help
>file.
Both of these are covered in the Mathematica Book which is included as part of the Help Browser. But since both the usage of "==" vs "=" and usage of {} to represent lists are fundamental Mathematica syntax, they are not documented again in the documentation for If.
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