Re: How to use GNU MP in octave?

[Mike Miller]

On Tue, 24 May 2005, Javier Arantegui wrote:

> > Let x = lg(8600!). Since lg(xy)=lg(x)+lg(y) you have
> >
> > x = sum(lg(k),k=1..86000)
> >
> > Define floor(x) as the integer part of x. Then
> >
> > 86000! = 10^(x-floor(x))*10^floor(x).
> >
> > You can evaluate x to the degree of accuracy you want, for example,
> > using Maple I got:
> >
> > 86000! = 7.91222558*10^372239
>
> Unfortunately, Octave doesn't buy the trick :-(:-(
>
> octave:4> k=1:1:86000;
> octave:5> x=sum(log10(k))
> x =  3.8702e+05
> octave:6> 10^(x-floor(x))*10^floor(x)
> ans = Inf


octave:2> format long
octave:3> X=1000;
octave:4> Y=sum(log10([1:X]))
Y = 2567.60464422213
octave:5> exponent=floor(Y)
exponent = 2567
octave:6> coeff = 10^(Y-floor(Y))
coeff = 4.02387260074868

Therefore, 1000! = 4.02387260074868 x 10^2567

Does that make sense?  Octave produces the coefficient and the exponent 
for you and you put them together.

If you want more precision, check this out:

http://maxima.sourceforge.net/

Mike