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Re: assuming certain properties about variables

  • To: mathgroup at smc.vnet.net
  • Subject: [mg111584] Re: assuming certain properties about variables
  • From: Derivator <salcedo at ugr.es>
  • Date: Fri, 6 Aug 2010 06:57:27 -0400 (EDT)
  • References: <i30gg9$mch$1@smc.vnet.net>

On 31 jul, 08:40, Benjamin Hell <h... at exoneon.de> wrote:
>   Hi,
> let's say I have defined the following function:
> f[x_?Positive] = x
> Now I want to evaluate f with a variable t:
> f[t]
> As mathematica knows nothing about t, the output is f[t] instead of t.
>
> How can I tell mathematica, that t should be a positive number so that
> Positive[t] evaluates true and then f[t] evaluates to t?
> Of course this is just an example, which should present what I would
> like to know.
>
> Thanks in advance.

I am not sure what you mean. Nevertheless, with
t/:Positive[t]=True;
you tell Mathematica t is positive. So, the input
{f[s],f[t]}
yields now
{f[s],t}

L.L.




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