On 7/24/2013 12:21 AM, Albert Rich wrote: > On Tuesday, July 23, 2013 2:32:20 PM UTC-10, da...@axiom-developer.org wrote: > >> We differ on some results because Rubi (or whatever program you are using >> to create the optimal results) assumes that square roots have only a single >> positive value. Axiom does not want to make this simplification so given >> sqrt(3)*sqrt(7)*sqrt(21) - 21 >> Axiom will not simplify this to zero but the Rubi test suite does. >
> Surly there must be a way to tell Axiom to choose the principal > branch so sqrt(4)-2 will simplify to zero? > > Albert >
I remember reading that some math people, 100 or 200 years ago, decided that sqrt (of non-negative, non-complex values) was single valued function and its value is the non-negative root (ie. principal square root).
Does any one have a reference if this is true and when this change was decided on? Or may be it always was like this?