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Re: complex math error? [message #4348 is a reply to message #4289]

Fri, 19 May 1995 00:00

thompson
Messages: 584
Registered: August 1991

Senior Member

llobet@elpp1.epfl.ch (Xavier Llobet i Sales EPFL-CRPP 1015 Lausanne CH) writes:

> In article <3pgkmo$b3s@post.gsfc.nasa.gov>, thompson@orpheus.nascom.nasa.gov
> (William Thompson) writes:

> [...]
> =I can't make it fail running IDL 3.6.1c under OSF/1 v2.0 on an AXP 3000/600
> =workstation. I always get the result
> =
> = IDL> print, exp( complex(0,1)*sqrt(2.)*10. )^sqrt(2.)
> = ( -1.28269e-10, 1.66070e-10)
> =
> =no matter how many times I try it. (I assume that's the correct value.)

> Nope. Just try

> IDL> print, exp( complex(0,1)*sqrt(2.)*10. )^sqrt(2.D0)
> ( -0.611276, 0.791417)

> This gives the right value.

> -xavier

Hmmm, when I tried this with IDL 3.6.1c I get

IDL> print, exp( complex(0,1)*sqrt(2.)*10. )^sqrt(2.D0)
( -0.0477381, -0.00519184)

Which is significantly different from either of the above. However, when I
tried this in a beta test version of IDL 4, I get

IDL> print, exp( complex(0,1)*sqrt(2.)*10. )^sqrt(2.D0)
( -0.61127603, 0.79141748)
IDL> print, exp( complex(0,1)*sqrt(2.)*10. )^sqrt(2.)
( -0.611276, 0.791418)

This seems to suggest that there is a bug in IDL v3.6 which is corrected in the
upcoming IDL v4. (Versions of IDL previous to 3.6 wouldn't have allowed the
above expression.)

Bill Thompson

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[Message index]

		complex math error? By: heard on Wed, 17 May 1995 00:00
		Re: complex math error? By: asb on Tue, 23 May 1995 00:00
		Re: complex math error? By: heard on Fri, 19 May 1995 00:00
		Re: complex math error? By: thompson on Fri, 19 May 1995 00:00

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