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.