Re: [Gretl-devel] matrix transposition/multiplication operator precedence

On Sat, 2 Jul 2016, Sven Schreiber wrote: >> "Kind of". But couldn't this be interpreted as a case of simple >> left-to-right evaluation in the absence of another deciding criterion? > > Well, I admit that according to table 3.1 in the command reference the > unary transpose and the binary transpose-multiply have the same priority, > and so it would boil down to left-to-right. > > But I'm not sure that's right. Semantically it's clear that > transpose-multiply just exists to mimick mathematical handwriting (on the > blackboard or on paper). So wherever it's meaningful, "'" must be replaced > by "'*". And then in the expression "a'*b'" the right precedence kicks in. > > Or to put it differently: Nobody would ever write "(a'b)'" on the > blackboard as "a'b'", because I think it's a broad consensus that the two > expressions are different. I agree with Sven on this, but OTOH what people expect on the basis of their mathematical background counts up to a point. The important thing is to stick as closely as possible to the principle of least surprise, which is, in turn, dictated by what other matrix-oriented languages do: as far as I can tell, the expression a'b' * is equivalent to (a') * (b') in Ox, Gauss and Julia * is illegal in Octave (which doesn't have, I think, the binary ' operator) so we're the exception. So I guess it's just another case of choice between backward-compatibility and pragamtism.