pow function problem

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cameyo
Posts: 176
Joined: Sun Mar 27, 2011 3:07 pm
Location: Italy
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pow function problem

Post by cameyo »

I have some problems with the pow function:

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(pow 3 0.33)
;-> 1.436977652184852
(pow -3 0.33)
;-> 1.#IND
In Mathematica (WolframAlpha):

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 3^0.33 = 1.436977652184852
-3^0.33 = -1.436977652184852
A simple solution:

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(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?

Lutz
Posts: 5289
Joined: Thu Sep 26, 2002 4:45 pm
Location: Pasadena, California
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Re: pow function problem

Post by Lutz »

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

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>>> 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.

cameyo
Posts: 176
Joined: Sun Mar 27, 2011 3:07 pm
Location: Italy
Contact:

Re: pow function problem

Post by cameyo »

Thanks for the explanation

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