Re: [Gretl-devel] matrix transposition/multiplication operator precedence
Am 01.07.2016 um 20:37 schrieb Allin Cottrell:
On Fri, 1 Jul 2016, Sven Schreiber wrote:
>
> <hansl>
> matrix a = zeros(3,1)
> matrix b = ones(2,3)
>
> matrix hu = a' * b'
> hu = a'(b')
> hu = a'b' # fails
> </hansl>
>
> Apparently gretl interprets the last line as "(a'b)'" which kind
of
> implies that the implicit multiplication with the transpose sign has
> higher precedence than the actual transposition of b.
"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.
thanks,
sven