Re: [Maxima-discuss] How do I translate the "ev" in "[a:b,b:c,c:d]; ev('[a,b,c],'a=42); " to a "subst"?

[Barton W. <wi...@un...>]

I use 'ev' to apply nouns, but not much else; for example:

(%i12) X : determinant(a);
(%o12) 'determinant(a)

(%i13) subst(a=matrix([1,2],[3,4]),X);
(%o13) 'determinant(matrix([1,2],[3,4]))

(%i14) ev(%,nouns);
(%o14) -2

The function 'makelist' is terribly useful, but I sometimes avoid it:

(%i15) load(integer_sequence)$

(%i16) map(lambda([q],q^2), 0 .. 9);
(%o16) [0,1,4,9,16,25,36,49,64,81]

--Barton
________________________________
From: Stavros Macrakis <mac...@gm...>
Sent: Monday, October 14, 2024 14:00
To: Eduardo Ochs <edu...@gm...>
Cc: <max...@li...> <max...@li...>; Robert Dodier <rob...@gm...>
Subject: Re: [Maxima-discuss] How do I translate the "ev" in "[a:b,b:c,c:d]; ev('[a,b,c],'a=42); " to a "subst"?

Caution: Non-NU Email

Internally makelist calls ev, but I've got to say that that shocks me even more than the fact that ev has bizarre behavior itself. In particular, I find this ridiculous:

makelist(['(x), '('x),'('('x))],'x,17,17) => [[17, '17, '('17)]]

Re using 'x as a variable in ev and makelist, I doubt that the implementers considered that case. It should probably raise an error.

Also, I don't know what you're trying to investigate by testing with ''a and ''''a. That syntax is evaluated at read, so those are precisely equivalent to b and c.

          -s


On Sun, Oct 13, 2024 at 7:00 PM Eduardo Ochs <edu...@gm...<mailto:edu...@gm...>> wrote:
On Sun, 13 Oct 2024 at 18:24, Stavros Macrakis <mac...@gm...<mailto:mac...@gm...>> wrote:
To elaborate a bit on what Robert said, I strongly discourage you from using ev programmatically if there is some other way to accomplish what you want.



Hi all,

I only tried to use ev because the documentation of makelist -
from here:

  (info "(maxima)makelist")
  https://maxima.sourceforge.io/docs/manual/maxima_21.html#makelist<https://urldefense.com/v3/__https://maxima.sourceforge.io/docs/manual/maxima_21.html*makelist__;Iw!!PvXuogZ4sRB2p-tU!E8DB51pqACvJJe_rDtXYKNRBji_gCK9BtGTqBoMiSOjdTMtKffAdNfCRz_CvJYxVrufSDCD_KhCb104$>

says this:

  The most general form, 'makelist (<expr>, <i>, <i_0>, <i_max>,
  <step>)', returns the list of elements obtained when 'ev (<expr>,
  <i>=<j>)' is applied to the elements <j> of the sequence: <i_0>,
  <i_0> + <step>, <i_0> + 2*<step>, ..., with <|j|> less than or
  equal to <|i_max|>.

and that gave me the impression that it was standard, or at least
common, to use ev to explain the semantics of special forms... but I
find ev very confusing - and I only tried to understand ev because
I tried this,

  [a:'b, b:'c, c:'d];                /* [b,c,d] */
  ['a, a, ''a, ''''a];               /* [a,b,c,d] */
  makelist([a,b,c],    'a, 42,43);   /* [[42,c,d], [43,c,d]] */
  makelist([a,b,c],     a, 42,43);   /* [[42,c,d], [43,c,d]] */
  makelist([a,b,c],   ''a, 42,43);   /* [[b,42,d], [b,43,d]] */
  makelist([a,b,c], ''''a, 42,43);   /* [[b,c,42], [b,c,43]] */

and I found the result of the first makelist very surprising.

Anyway: now I have many more things in my to-do list... I need to
finish some experiments with Sly/Slime (urgent), understand the last
messages by Robert and Stavros (urgent), and learn how to use trace
(not urgent). =/

  Cheers, thanks, etc...
    Eduardo