Limits & predicates with options.

*To*: mathgroup at smc.vnet.net*Subject*: [mg6999] Limits & predicates with options.*From*: Jack Goldberg <jackgold at math.lsa.umich.edu>*Date*: Thu, 1 May 1997 14:48:45 -0400 (EDT)*Organization*: Mathematics Department, University of Michigan*Sender*: owner-wri-mathgroup at wolfram.com

Hi folks: I need some guidance in handling this call: Limit[f[x,a],x->0] because the function f[x,a] is constructed deep inside other code. I want to take different actions depending on whether this limit exists. However, I don't know how to distinguish these alternatives without staring at the result. The problem seems to be that Limit can return a far larger set of outputs than I initially (and somewhat naively) thought. Besides the obvious, Limit can return this a*Inteval[-1,1] whose Head is Times. So "head" testing doesn't seem like a good idea. I am stuck here. What I would like ideally is a Predicate, say, LimitQ[...] which returns True if the limit exists and False otherwise. Of course, at this level of generality, one might have to wait forever for an answer! Which leads me to a second question. Can Predicates have options? In this case and obvious option would be a time constraint: The output is False, if CPU time exceeds a preset upper bound. Thanks all Jack Goldberg Mathematics University of Michigan