On Mon, 24 May 2010, James Limbouris wrote:
< On Mon, 24 May 2010 15:28:23 +0800, Leo Butler <l.butler at ed.ac.uk> wrote:
< >
< Here is a example from the problem I'm currently working on. I apologize for
< the length
< of the function, but it is difficult to imagine a simple one that will fail to
< evaluate.
<
< f(nr, ni) :=
< %i*((((%e^(-12.56637061435917*ni)*(-0.23518915858261*(nr^6-15*ni^2*nr^4+15*ni^4*nr^2-ni^6)-0.86386844040539*(6*ni*nr^5-20*ni^3*nr^3+6*ni^5*nr)-2.217486114751758*
< < snip >
< 1.841137478185708*(4*ni*nr^3-4*ni^3*nr)+64.83122366729704*(nr^3-3*ni^2*nr)+1.615197025742226*(3*ni*nr^2-ni^3)+72.8605673885606*(nr^2-ni^2)+13.8755315023416*ni*nr+
< 42.81053745639266*nr+6.616193944347959*ni+10.26849837929581)^(2))^(2))
<
< For the gory details see the attached .wxm file. Essentially, it is a nasty
< long mixture of polynomials, rationals and exponentials.
< I do not suspect it of being too numerically ill-conditioned to evaluate, and
< either of the following:
<
< f(2, 1);
< f(nr, ni), nr=2, ni=1, numer, keepfloat;
<
< will return a complex number instantly. Now lets try to get the modulus of
< this complex number:
<
< abs(f(2, 1))
< abs(f(2, 1)), numer;
< abs(f(nr, ni)), nr=2, ni=1, numer;
<
< all return instantly, while abs(f(nr, ni)) crashes with an out of memory
< error, after several minutes.
< Now the problem is,
<
< wxplot3d(f(nr, ni), [nr, 1, 2], [ni, 1, 2])
<
< will produce a plot, but
<
< wxplot3d(abs(f(nr, ni)), [nr, 1, 2], [ni, 1, 2]), numer;
<
< or
<
< wxplot3d('abs(f(nr, ni)), [nr, 1, 2], [ni, 1, 2]), numer;
<
Does
plot3d(lambda([nr,ni], abs(f(nr, ni))), [nr, 1, 2], [ni, 1, 2]);
work for you? I think the point is that you want to avoid any
simplification until you've actually substituted in values
for your arguments. Using a lambda function ought to do the
trick (on v5.21.1 at least).
Leo
--
The University of Edinburgh is a charitable body, registered in
Scotland, with registration number SC005336.