Right now I am writing a technical report, where I describe asymptotic(al) curves, expansions etc. My understanding after a bit of web browsing is that asymptotic and asymptotical are near-synonymous but the former is much more common (please correct me if I am wrong), so I will replace all instances of asymptotical by asymptotic.
Is there any general rule for those X vs. X-al situations? I can handle the most common cases (such as "Economic" vs. "economical") because I have seen them enough times, but I have not inferred a general rule, so I am at a loss when presented with an uncommon word (such as "asymptotic").
(I am not a native speaker.)