math.pow vs pow

[Clueless Moron]

Why do they act differently with respect to complex numbers?

Python 2.2.2 (#1, Feb 24 2003, 19:13:11)
[GCC 3.2.2 20030222 (Red Hat Linux 3.2.2-4)] on linux2
Type "help", "copyright" , "credits" or "license" for more information.[color=blue][color=green][color=darkred]
>>> pow(2, 0+1j)[/color][/color][/color]
(0.769238901363 97211+0.6389612 7631363475j)[color=blue][color=green][color=darkred]
>>>
>>> import math
>>> math.pow(2, 0+1j)[/color][/color][/color]
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: can't convert complex to float; use e.g. abs(z)[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

Apart from handling complex numbers, the built-in pow also has a
modulo efficiency hack.

When would I want to use math.pow?

[John J. Lee]

Re: math.pow vs pow

Clueless Moron <Bill.Gates@Mic rosoft.com> writes:
[color=blue]
> Why do they act differently with respect to complex numbers?[/color]
[...][color=blue]
> Apart from handling complex numbers, the built-in pow also has a
> modulo efficiency hack.
>
> When would I want to use math.pow?[/color]

For some applications, getting a complex result means you've made a
mistake. And some people don't know what a complex number is, and
would rather have their teeth drilled than find out.


John

You wouldn't know a subtle plan if it painted itself purple and danced
naked on top of a harpsichord singing 'Subtle Plans Are Here Again'

Blackadder

[Clueless Moron]

Re: math.pow vs pow

John J. Lee wrote:[color=blue]
> For some applications, getting a complex result means you've made a
> mistake. And some people don't know what a complex number is, and
> would rather have their teeth drilled than find out.[/color]

Perhaps, but why should pow() be different from math.pow() in python?

[Georgy Pruss]

Re: math.pow vs pow


"John J. Lee" <jjl@pobox.co m> wrote in message news:87k75lmlru .fsf@pobox.com. ..
| For some applications, getting a complex result means you've made a
| mistake. And some people don't know what a complex number is, and
| would rather have their teeth drilled than find out.

Can you provide an example when pow with real arguments gives a complex result,
please?

Georgy

|
|
| John
|
| You wouldn't know a subtle plan if it painted itself purple and danced
| naked on top of a harpsichord singing 'Subtle Plans Are Here Again'
|
| Blackadder

[Peter Otten]

Re: math.pow vs pow

Georgy Pruss wrote:
[color=blue]
>
> "John J. Lee" <jjl@pobox.co m> wrote in message
> news:87k75lmlru .fsf@pobox.com. ..
> | For some applications, getting a complex result means you've made a
> | mistake. And some people don't know what a complex number is, and
> | would rather have their teeth drilled than find out.
>
> Can you provide an example when pow with real arguments gives a complex
> result, please?[/color]

He could, if Python were not so reluctant:
[color=blue][color=green][color=darkred]
>>> pow(-5,.5)[/color][/color][/color]
Traceback (most recent call last):
File "<stdin>", line 1, in ?
ValueError: negative number cannot be raised to a fractional power

Sad day for the dentist:-)
But:
[color=blue][color=green][color=darkred]
>>> pow(complex(-5), .5)[/color][/color][/color]
(1.369151526412 4976e-16+2.2360679774 997898j)
[color=blue][color=green][color=darkred]
>>> pow(-5, complex(.5))[/color][/color][/color]
(1.369151526412 4976e-16+2.2360679774 997898j)

as you might expect.

Peter

[John J. Lee]

Re: math.pow vs pow

"Georgy Pruss" <see_signature_ _@hotmail.com> writes:
[color=blue]
> "John J. Lee" <jjl@pobox.co m> wrote in message news:87k75lmlru .fsf@pobox.com. ..
> | For some applications, getting a complex result means you've made a
> | mistake. And some people don't know what a complex number is, and
> | would rather have their teeth drilled than find out.
>
> Can you provide an example when pow with real arguments gives a complex result,
> please?[/color]
[...]

I was thinking about results of earlier calculations providing the
argument for pow.


John