OpenEuphoria

RE: logs and antilogs

• Posted by Andy Serpa <ac at onehorseshy.com> Oct 26, 2002
• 479 views

I forgot antilogs.

Antilogs are just the inverse of log.


The standard exp() function is the same as the natural antilog.  More 
generally, the antilog is the base raised to the power of the logarithm.

The base of natural logs is Euler's number, which is:

E = 2.718281828459045235 ...





Andy Serpa wrote:
> 
> Kat wrote:
> > I have been looking all over the net for a formula to calculate logs and 
> > 
> > 
> > antilogs for any given number, but turned up zip. Can anyone suggest a 
> > formula?
> > 
> > Kat
> > 
> > 
> Found this on web, and translated to Euphoria:
> 
> -- natural logarithm
> function ln(atom x)
> atom precision,l,m,n,k,val
> 
>     if x <= 0.0 then
>         -- ERROR: can't take a log of zero or negative
>         -- return some appropriate error here (like a sequence)
>         -- or kill program
>     end if
> 
>     precision = 1e-15
> 
>     m = 1.0
> 
>     n = 0.0
>     while (x/m >= 10.0) do
>         m *= 10.0
>         n += 1.0
>     end while
> 
>     if x < 1.0 then
>         n = 0.0
>         while (x/m <= 0.1) do
>             m *= 0.1
>             n -= 1.0
>         end while
>     end if
> 
>     x /= m
>     x = (x-1)/(x+1)
>     l = x
>     val = x
> 
> 
>     k = 3.0
> 
>     l *= x*x
>     m = l/k
>     val += m
> 
>     if m < 0.0 then
>         m = -m
>     end if
> 
>     while (m >= precision) do
>         k += 2.0
>         l *= x*x
>         m = l/k
>         val += m
> 
>         if m < 0.0 then
>             m = -m
>         end if
>     end while
> 
>     val = (val * 2) + (n*2.30258509298749)
> 
>     return val --  / 2.30258509298749 (uncomment to get log10)
> 
> end function
> 
> 
> -- returns base-based logarithm of x
> function logbase(atom x, atom base)
>     return ln(x)/ln(base)
> end function
> 
>