Re: Error message need explaination in english
- To: mathgroup at smc.vnet.net
- Subject: [mg78673] Re: Error message need explaination in english
- From: David Bailey <dave at Remove_Thisdbailey.co.uk>
- Date: Fri, 6 Jul 2007 03:34:12 -0400 (EDT)
- References: <f6if0b$428$1@smc.vnet.net>
JGBoone at gmail.com wrote:
> So i put in these commands
>
> Q=Range[10];
> size[group_]=Length[group];
> metareplace[group_] := (group[[Random[Integer, {1, size[group]}]]] =
> hubl[metacommunity]);
> (*takes random element of community size and replaces it with random
> element of metacommunity by way of the function hubl[group_]*)
> metareplace[Q]
>
>
> and get this error message
>
> Set::setps: {1, 2, 3, 4, 5, 6, 7, 8, 9, 10} in assignment of part is
> not a symbol
>
> looking at the help menu only confuses me further. can anyone tell me
> in layman's terms what the messages means?
> thanks
>
>
This is a common error. It happens because you are passing the value of
Q to metareplace - not Q itself - so that you end up executing something
like
{1,2,3,4,5,6,7,8,9,10}[[7]]=something;
One solution is to stop your function evaluating its argument by using
SetAttributes[metareplace, HoldAll];
There is another apparent problem with your code however, because your
definition of 'size' should use := - otherwise the RHS is evaluated to 0
once and for all.
David Bailey
http://www.dbaileyconsultancy.co.uk