Re: assuming certain properties about variables
- To: mathgroup at smc.vnet.net
- Subject: [mg111437] Re: assuming certain properties about variables
- From: Murray Eisenberg <murray at math.umass.edu>
- Date: Sun, 1 Aug 2010 04:57:43 -0400 (EDT)
But once you put the restriction on the argument of f, you've told Mathematica not to carry out the evaluation of f unless the input supplied is actually positive. If now t is just a symbol, then it is not positive (and not negative, either) -- it's just a symbol. So why would you expect to be able to tell Mathematica that it's positive? In general, Mathematica variables don't really have types. If it's just the particular symbol t that you want to supply to f, then you could do this (I'm changing your function definition for clarity) -- not that you probably want SetDelayed (:=) instead of Set (=): f[x_?Positive] := x^2 f[t] = t^2; f[3] 9 f[t] t^2 t = -5; f[t] f[-5] f On 7/31/2010 2:40 AM, Benjamin Hell wrote: > > 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. -- Murray Eisenberg murray at math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower phone 413 549-1020 (H) University of Massachusetts 413 545-2859 (W) 710 North Pleasant Street fax 413 545-1801 Amherst, MA 01003-9305