Usage of “symmetrical” and “symmetric”

What is the appropriate usage of "symmetrical" and "symmetric" (using the geometrical adjectival definition of both terms)? Are they synonymous?

Dictionary:

Merriam-Webster lists symmetric as being a variant of symmetrical, which is the 'official' dictionary entry:

symmetrical, adj : 1 : having or involving symmetry : exhibiting symmetry : exhibiting correspondence in size and shape of parts : BALANCED, REGULAR {the human body issymmetrical} {crystals are often symmetrical} {a symmetrical garden} {a symmetricalgrouping}

Discussion:

Sam Lisi:  At least in a mathematical context, I think "symmetric" is far more common. For one thing, there are many technical terms where "symmetric" is the correct choice (e.g. "symmetric space", "symmetric relation", "symmetric group"). I can't think of any technical term including "symmetrical".

user16269: "Symmetrical" is a non-technical term, to describe any object that has symmetry; for example, a human face. "Symmetric" means "relating to symmetry", and is also used in a number of technical mathematical contexts (see Sam Lisi's comment under the question).

JLG: I don't agree with symmetrical being a nontechnical term. Dorland's Medical Dictionary lists only "symmetrical," and the definition is: "pertaining to or exhibiting symmetry; in chemistry, denoting compounds which contain atoms or groups at equal intervals in the molecule." (Sounds technical to me.)

naught101:mitch, because symmetric is defined as "symmetrical" - I assume that's supposed to mean it's a perfect synonym.

mitch: naught101: 1) there are no perfect synonyms. Ever. And a crowd sourced definition ain't gonna specify enough to judge. 2) wiktionary is not definitive. Don't take anything it says as gospel or draw logical conclusions from it. Frankly the same could be said for the OED, but wiktionary is not written by people who have spent a long time judging such things.

Related: 

“electric” vs. “electrical”, “symbolic” vs. “symbolical”, “scientific” vs. “scientifical”,

and the most excellent general discussion Why is it “geometric” but “theoretical”?

asymmetric and unsymmetrical :http://emuch.net/html/201206/4592142.html

asymmetric是不对称，一般化合物含义手性中心，unsymmetrical非对称，一般化合物不含有手性中心