Re: Testing Mathematica Expressions?
- To: mathgroup at smc.vnet.net
- Subject: [mg106614] Re: Testing Mathematica Expressions?
- From: Noqsi <jpd at noqsi.com>
- Date: Mon, 18 Jan 2010 02:36:38 -0500 (EST)
- References: <email@example.com>
On Jan 17, 5:13 am, AES <sieg... at stanford.edu> wrote: > 5) Is ToExpression["exprx"] /. ruleOne really exactly the same thing > (or, will it produce exactly the same results) as exprx /. ruleOne? That you even ask this question shows that you simply haven't done your homework. Please study the tutorials listed at: tutorial/ExpressionsOverview in the Documentation Center. Many programming systems (including Mathematica) feature powerful string pattern and replacement capabilities. The most common approach is so-called "regular expressions", which after >40 years of refinement are extremely flexible and powerful for text processing. In principle, they could be used for computer algebra, but in practice they are impractical. The amusing http://blog.stevenlevithan.com/archives/algebra-with-regexes starts out "Regexes suck at math". In Mathematica, Replace is not the same as StringReplace. Indeed, they are very different, and their application areas are almost disjoint. Computer algebra is necessarily more formal and mechanical than human algebra. Wolfram has done a great job of presenting the underlying structures in a comprehensible way to a human user, but there are practical limits. And often, as a human user, you need to access that formal, mechanical level to unambiguously program Mathematica for particular tasks, so completely hiding it would be a disaster. The checkered history of generalized functions in Mathematica should serve as a cautionary example to those who believe that attempting heuristic decoding of user intentions is a good idea in any but the shallowest situations. See: http://forums.wolfram.com/mathgroup/archive/2009/Jun/msg00180.html for further discussion of this issue.