Meanwhile, there's an analytic form based on figuring out how many factors
of 10 and 2x5s there are...
On 3/27/08, bill lam <[EMAIL PROTECTED]> wrote:
>
> You need to add the trailing 'x' to the formatted number.
> I'm unskillful in writing tacit form but the following seems implementing
> your
> logic.
> _5{. |. ": ". ,&'x' |. ": */ 1+i.10x
> 36288
> _5{. |. ": ". ,&'x' |. ": */ 1+i.20x
> 17664
> _5{. |. ": ". ,&'x' |. ": */ 1+i.10050x
> 69696
>
> btw I think that ! should be more efficient than */@:>:@:i.
>
>
> Geoff Canyon wrote:
> > I'm trying to find the last five non-zero digits of a large factorial.
> > So for:
> >
> > !10x = 3628800
> >
> > the answer would be 36288 while for:
> >
> > !20x = 2432902008176640000
> >
> > the answer would be 17664.
> >
> > I'm trying to do this by calculating /* 1+i.1000 without calculating
> > large numbers by losing the trailing zeroes at each step and the leading
> > digits more than five. Here's what I have so far:
> >
> > (((|.&.":)@(5{.":&(|.&.":)))@*)/ 1+i.20x
> >
> > The truncating code:
> >
> > -- Converts to string, transposes, and converts back to a number. That
> > loses trailing zeroes (because they're now leading zeroes).
> > -- Converts to string and grabs the first five characters (which were
> > the last five non-zero digits).
> > -- Converts to string again -- not sure why this is necessary, but it
> > doesn't work otherwise -- transposes, and converts back to a number.
> >
> > This whole thing is performed atop *, and the resulting verb is inserted
> > into the list from 1 to a large number.
> >
> > This seems to work for large numbers up to 10049x. At 10050x I get an
> > ill-formed number error.
> >
> > Where did I go wrong?
> >
> > regards,
> >
> > Geoff
> > ----------------------------------------------------------------------
> > For information about J forums see http://www.jsoftware.com/forums.htm
> >
>
> ----------------------------------------------------------------------
> For information about J forums see http://www.jsoftware.com/forums.htm
>
--
Devon McCormick, CFA
^me^ at acm.
org is my
preferred e-mail
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