[Maxima-bugs] [ maxima-Bugs-1735401 ] makelist( ) inside function definition

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Bugs item #1735401, was opened at 2007-06-11 16:27
Message generated for change (Comment added) made by woollett
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Category: Lisp Core
Group: None
Status: Closed
Resolution: Wont Fix
Priority: 5
Private: No
Submitted By: Ted Woollett (woollett)
Assigned to: Nobody/Anonymous (nobody)
Summary: makelist( ) inside function definition

Initial Comment:
Attempts to use makelist function inside a user defined function:

Maxima 5.12.0 http://maxima.sourceforge.net
Using Lisp GNU Common Lisp (GCL) GCL 2.6.8 (aka GCL)
/*   1  */
(%i1) table1(expr, n, n1, n2) := (
     z :  makelist(expr, n, n1,n2 ),
     print(" z = ", z) )$

(%i2) table1(n^2, n, 1, 3)$
        2   2   2
 z =  [n , n , n ]

/*   2   */
(%i3) table2(expr,n,n1,n2) := (
  print(" expr = ",expr," n = ",n," n1 = ",n1," n2 = ",n2),
  z : makelist(expr,n,n1,n2),
  print(" z = ", z) )$

(%i4) table2(n^2,n,1,3)$
          2
 expr =  n   n =  n  n1 =  1  n2 =  3
        2   2   2
 z =  [n , n , n ]

/*     3     */
(%i5) table3(expr,n,n1,n2) := block([z],
  print(" expr = ",expr," n = ",n," n1 = ",n1," n2 = ",n2),
  z : makelist(expr,n,n1,n2),
  print(" z = ", z) )$

(%i6) table3(n^2,n,1,3)$
          2
 expr =  n   n =  n  n1 =  1  n2 =  3
        2   2   2
 z =  [n , n , n ]

/*       4      */
(%i7) table4(expr,n,n1,n2) := block([z,m1:n1, m2:n2],
       print(" expr = ",expr," n = ",n," m1 = ",m1," m2 = ",m2 ),
       z : makelist(expr, n, m1, m2),
       print(" z = ", z) )$

(%i8) table4(n^2, n, 1, 3)$
          2
 expr =  n   n =  n  m1 =  1  m2 =  3
        2   2   2
 z =  [n , n , n ]
 I am assuming "expr" is not a reserved word in Maxima. 
Perhaps I am not using corrent passage of arguments??

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Comment By: Ted Woollett (woollett)
Date: 2007-06-15 13:48

Message:
Logged In: YES 
user_id=1806103
Originator: YES

Can we add a comment after a thread is "closed"??

Thanks for the explanation of forcing evaluation with ev(). I clearly need
to pay closer attention to R. Dodier's "Minimal Maxima" discussion of these
issues.

Was initially trying to make something like Mathematica's Table function.
The following works but retains brackets if expr is [n, n^2].

(%i7) mytable(expr,n, [nval] ) :=
      map( disp,  ( if length(nval) = 2 then
               makelist( ev(expr),n, nval[1], nval[2] ) else
                  makelist( ev(expr) , n, nval[1] ) ) ) ;


----------------------------------------------------------------------

Comment By: Robert Dodier (robert_dodier)
Date: 2007-06-14 18:24

Message:
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Originator: NO

It turns out that the observed behavior is to be expected. Maxima does not
try as much as it can to evaluate expressions; variables in expressions are
evaluated just once. This policy makes it easier to predict results, at the
cost of some surprise.

makelist evaluates its first argument, expr, for each value of n between
n1 and n2. What is the value of expr? It is n^2 in each case. That is not
evaluated further, so the result is [n^2, n^2, n^2].

There are various ways to cause expr to be evaluated more. Here is one.

my_table (expr, n, n1, n2) := makelist (ev (expr), n, n1, n2);

my_table (n^2, n, 1, 3);
 => [1, 4, 9]

Although Maxima's evaluation rules are complex and often confusing, I'm
closing this report as "won't fix".

Hope this helps.
Robert Dodier

----------------------------------------------------------------------

Comment By: Ted Woollett (woollett)
Date: 2007-06-11 16:37

Message:
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Originator: YES

my computer system:

Maxima version: 5.12.0
Maxima build date: 19:33 5/3/2007
host type: i686-pc-mingw32
lisp-implementation-type: GNU Common Lisp (GCL)
lisp-implementation-version: GCL 2.6.8


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