Dan <vi5u0-maxima at yahoo.co.uk> writes:
> Imagine I do something like (a more complicated version of) this
>
> load(draw) ;
>
> f(x) := 4*x^5 ;
> g(x) := 3*x^4 ;
>
> h(x) := ev(f(x)/g(x)) ;
>
> draw2d(explicit(h(x),x,0,7)) ;
>
> If I've understood correctly, the ev() is called separately for each
> specific numerical value of x during the draw2d(). A lot of
> CPU time could be saved by instead calling the ev()
> once and for all at the time h(x) is defined. Is this possible,
> please?
I presume that you want to use the ev() call to simplify the
polynomials. Have you considered using a different function like
ratsimp()?
Anyway, the problem for you is that := doesn't evaluate its RHS by
default. To force it to do so, you can use the ''( <blah> )
construction. See the definition of h3 below.
Rupert
(%i1) f(x) := 4*x^5;
5
(%o1) f(x) := 4 x
(%i2) g(x) := 3*x^4;
4
(%o2) g(x) := 3 x
(%i3) h1(x) := ev(f(x)/g(x));
f(x)
(%o3) h1(x) := ev(----)
g(x)
(%i4) h1(3);
(%o4) 4
(%i5) h2(x) := f(x)/g(x);
f(x)
(%o5) h2(x) := ----
g(x)
<snip>
(%i7) h2(3);
(%o7) 4
(%i8) h3(x) := ''(ev(f(x)/g(x)));
4 x
(%o8) h3(x) := ---
3
(%i9) h3(3);
(%o9) 4
(%i10)
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