# [Maxima] define bug?

Stavros Macrakis macrakis at alum.mit.edu
Sun Jan 15 16:20:26 CST 2012

```The key to the answer is "define works fine".

The ":=" operator -- like function definition in all ordinary programming
languages -- defers the evaluation of its arguments until the function is
called.

The "define" function evaluates the right-hand side (also the left) *at the
time of definition*.

For example:

(%i1) f(x):=print(x);
(%o1)                             f(x) := print(x)          <<< function
definition includes "print"
<<< no printing
(%i2) f(4);
4                        <<< print when *evaluating* f
(%o2)                                 4

(%i3) define('(g(x)),print(x));
x                       <<< print when *defining* g
(%o3)                             g(x) := x         <<< function definition
does not include "print"
(%i4) g(4);
(%o4)                                 4

Doing something like

h(x) := diff(f(x),x)

will then try to evaluate diff(f(4),4), which is of course nonsensical.

-s

On Fri, Jan 13, 2012 at 15:36, Hans W. Hofmann <hawe at chefmail.de> wrote:

> (%i2) f(x):=-k*x^3+3*k^2*x^2;
>                                         3      2  2
> (%o2)                    f(x) := (- k) x  + 3 k  x
>
> (%i3) df(x):=diff(f(x),x)\$ df(x);
>                                   2          2
> (%o3)                          6 k  x - 3 k x
>
> (%i4) df(k)=3;
>                                      3
> (%o4)                             8 k  = 3
>
> whats this? should have
>
> (%i5) 6*k^2*x-3*k*x^2 = 3, x=k;
> (%o5) 3*k^3 = 3
>
> using define all works fine....
>
> Gruß HW
>
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