plot2d and quad_qags feeding non-numeric input to user function

You need to quote the argument:

    plot2d( '( bell(x) ), [x,-1,1]);

If quoting weren't required, you couldn't do (e.g.)  plot2d(
taylor(sin(x),x,0,3), [x, 0, 3] ) -- Maxima would have no way of knowing
whether you wanted taylor(sin(x),x,0,3) plotted for each value of x (which
would be an error) or the *result* of taylor(...) = x-x^3/6 plotted at each
value of x.

           -s

On Tue, Jul 26, 2011 at 11:55, Charles Russell <worwor at bellsouth.net> wrote:

> I can't use the following user-defined function in the numerical procedures
> plot2d and quad_qags because they feed it non-numeric values as input.  In
> the case of plot2d I can get around this with a discrete plot, but I can't
> find a workaround for the numeric integration. (This is an easy example to
> integrate analytically, but I am interested in the general case.)
>
> bell(x):= block([dum],
>     if not numberp(x) then print("bell: error, x = ",x),
>     if x <= -1 then dum : 0
>     else if x >= 1 then dum : 0
>     else dum : (1 - x^2)^2,
>     return(dum)
>     ) ;
>
> plot2d(bell, [x,-1,1]); /* OK */
> trace(bell);
> plot2d(bell(x), [x,-1,1]); /* input non-numerical */
> qags_out: quad_qags(bell(s), s, -1, 1); /* input non-numerical */
>
> (%i83) trace(bell);
> (%o83)                              [bell]
> (%i84) plot2d(bell(x), [x,-1,1]); /* input non-numerical */
> 1 Enter bell [x]
> bell: error, x =  x
> 1 Exit  bell dum
> COERCE-FLOAT-FUN: no such Lisp or Maxima function: dum
>  -- an error. To debug this try: debugmode(true);
> (%i85) qags_out: quad_qags(bell(s), s, -1, 1); /* input non-numerical */
> 1 Enter bell [s]
> bell: error, x =  s
> 1 Exit  bell dum
> COERCE-FLOAT-FUN: no such Lisp or Maxima function: dum
>  -- an error. To debug this try: debugmode(true);
>
> I've tried converting the input with ev(x,numer) but that doesn't work:
>
> /* lbell(x) := bell(log(x))/x; */
> lbell(x) := block(
>     [xn: ev(x,numer,infeval)],
>     if not numberp(xn) then print("lbell: error, xn = ",xn),
>     bell(log(xn))/xn
>     );
>
> (%i34) plot2d(lbell(x),[x, 0.01, 10]);
> lbell: error, xn =  x
>
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