math.exp(complex)

[David Eppstein]

Why doesn't this work?
[color=blue][color=green][color=darkred]
>>> import math
>>> math.exp(1j*mat h.pi)[/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)

The expected answer, of course, is -1.

It does work if you do it like this:
[color=blue][color=green][color=darkred]
>>> math.e**(1j*mat h.pi)[/color][/color][/color]
(-1+1.22464679914 73532e-16j)

So why not math.exp(comple x)?

--
David Eppstein http://www.ics.uci.edu/~eppstein/
Univ. of California, Irvine, School of Information & Computer Science

[Raymond Hettinger]

Re: math.exp(comple x)

[David Eppstein][color=blue]
> Why doesn't this work?
>[color=green][color=darkred]
> >>> import math
> >>> math.exp(1j*mat h.pi)[/color][/color]
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> TypeError: can't convert complex to float; use e.g. abs(z)
>
> The expected answer, of course, is -1.
>
> It does work if you do it like this:
>[color=green][color=darkred]
> >>> math.e**(1j*mat h.pi)[/color][/color]
> (-1+1.22464679914 73532e-16j)
>
> So why not math.exp(comple x)?[/color]

Use the cmath module for complex ops:

[color=blue][color=green][color=darkred]
>>> import cmath
>>> import math
>>> cmath.exp(1j*ma th.pi)[/color][/color][/color]

(-1+1.22460635382 23773e-016j)


Raymond Hettinger

[John J. Lee]

Re: math.exp(comple x)

David Eppstein <eppstein@ics.u ci.edu> writes:
[color=blue]
> Why doesn't this work?
>[color=green][color=darkred]
> >>> import math
> >>> math.exp(1j*mat h.pi)[/color][/color]
> Traceback (most recent call last):[/color]
[...][color=blue]
> So why not math.exp(comple x)?[/color]

import cmath as math

:-)


John

[David Eppstein]

Re: math.exp(comple x)

In article <ENnbb.10075$Uv 2.662@nwrdny02. gnilink.net>,
"Raymond Hettinger" <vze4rx4y@veriz on.net> wrote:
[color=blue][color=green]
> > So why not math.exp(comple x)?[/color]
>
> Use the cmath module for complex ops:[/color]

Thanks, but then my next question is, why are math and cmath different
from each other?

And, is there any important difference (e.g. in numerical accuracy)
between cmath.exp(x) and math.e**x ?

--
David Eppstein http://www.ics.uci.edu/~eppstein/
Univ. of California, Irvine, School of Information & Computer Science