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Title: pow function problem
Post by: cameyo on October 19, 2020, 02:11:55 AM

I have some problems with the pow function:

Code Select Expand
(pow 3 0.33)
;-> 1.436977652184852
(pow -3 0.33)
;-> 1.#IND

In Mathematica (WolframAlpha):

Code Select Expand
 3^0.33 = 1.436977652184852
-3^0.33 = -1.436977652184852

A simple solution:

Code Select Expand
(define (pow-ext x n)
  (if (< x 0)
      (sub 0 (pow (sub 0 x) n))
      (pow x n)))
(pow-ext 3 0.33)
;-> 1.436977652184852
;(pow-ext -3 0.33)
;-> -1.436977652184852

Why newLISP result is 1.#IND?

Title: Re: pow function problem
Post by: Lutz on October 19, 2020, 08:24:17 AM

The newLISP function pow works like the Perl and Python function pow:

Code Select Expand

>>> pow(3, 0.33)
1.4369776521848516
>>> pow(-3, 0.33)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: negative number cannot be raised to a fractional power
>>>

All use the Standard C Library function pow(a,b) using double floats.

Title: Re: pow function problem
Post by: cameyo on October 19, 2020, 12:25:46 PM

Thanks for the explanation

newLISP Fan Club

Forum => newLISP in the real world => Topic started by: cameyo on October 19, 2020, 02:11:55 AM