Re: Bizarre semantic of Mat

[Loïc Grenié <loic.grenie@gmail.com>]

On Thu Jan 18th, 2024, at 08:19, Ilya Zakharevich wrote:

On Wed, Jan 17, 2024 at 11:31:39AM +0100, Bill Allombert wrote:
> > Is there a simple way to convert a vector-column into a 1 column
> > matrix (without using matrix())?  Mat() is almost there — except for
> > bizarre special-cases — which are impossible to switch off!
>
> There is a trick:
>
> ? V=[[1]~,[2]~,[3]~]
> %28 = [[1]~,[2]~,[3]~]
> ? Mat(V~)~
> %29 = Mat([[1]~,[2]~,[3]~])

Hmm?  It seems that this is “another ‘cute special case’” — which
requires PRIOR KNOWLEDGE about the nature of elements of the vector.
Does not it?

    I don't know what you intend to do. However if you have a column

  C the content of which is unknown, then you have two reasonable ways

  to transform it in a #C\times1 matrix:

matrix(#C,1,a,b,C[b])

Mat(vector(1,a,C))

  You don't want the first and you name the second ugly, that's your

  call. Just don't expect the developers of pari/gp to write the function

  you wish.

  Observe that the condition "I don't know what is in my column vector

  but I want a column-matrix out of it" is not the typical situation; usually

  one *knows* what is in the column (and can decide what to do). Observe

  also that the first solution is completely reasonable, documented. I think

  you are wasting time and bandwidth on this one.

       Loïc