Re: [Gretl-users] pre-multiplication by transpose

On Fri, 7 Dec 2012, Sven Schreiber wrote: > On 12/07/2012 08:31 PM, Alan G Isaac wrote: >> On 12/7/2012 1:52 PM, Summers, Peter wrote: >>> But your example holds true whether or not we write x'y or x'*y >> >> >> Absolutely. I was addressing only the issue of >> how to handle a 1 x 1 matrix, not the core question. >> >> I agree that many matrix programming languages special case >> the 1x1 matrix. I guess it is convenient enough to introduce >> the risk I illustrated, at least in the opinion of some. >> Not in mine. >> >> I also have an opinion the topic question (explicit is better than implicit), >> but not a strong one. One thing is for sure, x'*y needs to be legal. >> The question is whether x'y is a legal "shorthand". > > To me it would seem that if somebody writes <m'>, the script author is > treating m as a matrix. Because why would you use a transpose if the > object is always expected to be a scalar? Therefore it would seem > appropriate to always treat <m'y> as a matrix multiplication even in the > special case when m is 1x1. FWIW, I think that's the explanation of gretl's current inconsistency. If you write "X'Y" it seems clear that you really intend a matrix operation, with two matrix operands, in which case a 1x1 matrix would not be given special treatment with regard to conformability. But if you write "X'*Y", with X 1x1, gretl first evaluates X', producing an anonymous 1x1 matrix, then finds plain multiplication, and applies the idea that 1x1 matrices can count as scalars if need be.