Re: [boost] [units] - learning to use, continued :)

Subject: Re: [boost] [units] - learning to use, continued :)
From: Janek Kozicki (janek_listy_at_[hidden])
Date: 2011-11-30 10:45:22

Paul A. Bristow said:     (by the date of Wed, 30 Nov 2011 11:08:53 -0000)

> > - find some arbitrary precision library, that will work with Units
> >   and VERY big factorials, like 100! or even better 1000!
> 
> There are indeed at least two related efforts on arbitrary precision library going on.
> 
> A multiprecision library by Christopher Kormanyos based on his e_float library which is in the
> sandbox .
> 
> and, based on this, an extension to Boost.Math (already user-defined type ready and able to use NTL
> and GMP) that John Maddock is currently busy working on.
> 
> These should allow you to calculate factorial 100! to a few hundred decimal digits.
> 
> For your amusement, 100! is (to 50 decimal digits)
> 
>   100! = 9.332621544394415268169923885626670049071596826438162146859e+157

I'm using apcalc, a very nice software ;-)

933262154439441526816992388562667004907159682643816214685929638952175999932\
29915608941463976156518286253697920827223758251185210916864000000000000000000000000

 
> But I'm not at all sure that this is the way forward for your purpose.  For example, in calculating
> gamma functions, it is customary to use logs to avoid overflow.
> 
> And we need to make sure we can walk before we can run - combining arbitrary precision with
> Boost.Units (where double precision is usually enough to represent the accuracy of physical things).

hmm, you are right. I probably will need to go into logs.

Boost.Units has no effect on runtime, it checks units during
compilation. So using them shouldn't affect at all.

I'm glad that I installed 1.48 with Steven's help. And now I can
convert my code to use units :)

first thing will be to figure out how to declare a type meter^-0.5
maybe my previous try that didn't work with boost 1.42 will start to work with 1.48:

typedef derived_dimension<length_base_dimension,root<2> >::type quantum_wavefunction_1D;

best regards
-- 
Janek Kozicki                               http://janek.kozicki.pl/