OpenEuphoria

Re: power overflow

• Posted by jluethje at gmx.de Jun 02, 2002
• 431 views

Ooops,

I forgot to mention the 3rd function.

>> I get this error message:

>> C:\MyProj\Euphoria\TSLibrary\TSLibrary_Formula_Finder.e:232 in function
>> power_()
>> math function overflow error
>>     a = 24
>>     b = 576


>> where power (a,b) is executed

>> How can I check parameters a and b and not execute power() if they are too
>> big (especially b)?
>> I guess one way is to write my own version of power()?


> This is a snippet from my private file math.e:

> ------------------------------------------------------------------------
> global function ln (object x)
> -- Euphoria's built-in log() function
> -- (= logarithm for base e = natural logarithm)

>    return log(x)
> end function


> without warning
> global function log (atom b, object x)
> -- general log() function
> -- logarithm for base b and number (or sequence) x
> -- Note: built-in routine log() redefined

> -- in : b: positive real number, != 1
> --      x: positive real number (or sequence of those numbers)
> -- out: real number
--      (x = 1  -->>  function returns 0 for any base b)

>    return ln(x)/ln(b)
> end function
> with warning
> ------------------------------------------------------------------------

> Given this general log() function,

> y = power(a, b) is equivalent to

> b = log(a, y) .

> When we know the maximum numeric value, that Euphoria can handle
> (y_max), then we have:

> b_max = log(a, y_max) .

> After refman_2.htm, y_max = +1e300, i.e.

> -------------------------
> b_max = log(a, +1e300)
> -------------------------

> When a = 24 (as in your example above), b cannot be more than

> b_max = log(24, +1e300) = 217.36 .

> So you can see, that b = 576 is much too big.


> Now we check the calculation:

> y = power(24, 217.36) = 1.006272255e+300

> OK 


The 3rd function in this context is:

a = power(y, 1/b) .

This means,
a_max = power(y_max, 1/b)

--------------------------
a_max = power(+1e300, 1/b)
--------------------------

When b = 576 (as in your example above), a cannot be more than

a_max = power(+1e300, 1/576) = 3.32 .

So you can see, that a = 24 is much too big.


Checking the calculation gives:

y = power(3.32, 576) = 1.498084165e+300


That's OK, and we see, that +1e300 is only *roughly* the biggest number,
that Euphoria can handle.

Best regards,
   Juergen