| Re: Inconstant log(-1) handling [message #957 is a reply to message #844] |
Tue, 27 April 1993 13:19  |
dit
Messages: 5
Registered: July 1992
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Junior Member |
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In article <C64BH2.Ex0@murdoch.acc.Virginia.EDU>,
gsh7w@fermi.clas.Virginia.EDU (Greg Hennessy) writes:
> I strongly get the idea that this is one of those "Doctor, it hurts
> when I do this." "Don't do that." type posts, but here it goes. In IDL
> v3.0.0 on a sparcstation 10, running 4.0.3b there seems to be an
> inconsistency with how logarithms of negative numbers are done. Don't
> sugguest that I shouldn't be doing this in the first place, I know I
> shouldn't, however what IDL is giving me seems a tad bit weird. I do
> know that if I do a
> IDL>tmp=check_math(trap=0) & delvar,tmp
> in my startupfile, IDL returns NaN's for the illegal values, but it
> does not seem to do so by default.
>
> Greg Hennessy
>
>
>> idl
> IDL. Version 3.0.0 (sunos sparc).
> Copyright 1989-1992, Research Systems, Inc.
> All rights reserved. Unauthorized reproduction prohibited.
> Site: 2762.
> Licensed for use by: UVA (Perseus)
>
> % Compiled module: CINIT.
> SUNIDL>x=findgen(6)-3
> SUNIDL>print,x
> -3.00000 -2.00000 -1.00000 0.00000 1.00000 2.00000
> SUNIDL>print,alog10(x)
> % Program caused arithmetic error: Floating illegal operand
> % Detected at $MAIN$ (ALOG10).
> % Program caused arithmetic error: Floating divide by 0
> % Detected at $MAIN$ (ALOG10).
> 200000. 200000. 200000. 0.00000 0.00000 0.301030
> SUNIDL>print,alog10(x)
> % Program caused arithmetic error: Floating illegal operand
> % Detected at $MAIN$ (ALOG10).
> % Program caused arithmetic error: Floating divide by 0
> % Detected at $MAIN$ (ALOG10).
> 1.00000 1.00000 1.00000 0.00000 0.00000 0.301030
> SUNIDL>
>
That's what I've just seen running this test on a VAX under OpenVMS 5.5-2
with no Check_Math set (IDL's default):
; IDL Version 3.0.0 (vms vax)
; Journal File for VAXSER::SYSTEM
; Working directory: SYS$SYSROOT:[SYSMGR]
; Date: Tue Apr 27 22:03:48 1993
x=findgen(6)-3
print,x
; -3.00000 -2.00000 -1.00000 0.000000 1.00000 2.00000
print, alog10(x)
; % Program caused arithmetic error: Logarithm of 0 or negative
; % Program caused arithmetic error: Logarithm of 0 or negative
; % Program caused arithmetic error: Logarithm of 0 or negative
; % Program caused arithmetic error: Logarithm of 0 or negative
; 0.000000 0.000000 0.000000 0.000000 0.000000 0.301030
print, alog10(x)
; % Program caused arithmetic error: Logarithm of 0 or negative
; % Program caused arithmetic error: Logarithm of 0 or negative
; % Program caused arithmetic error: Logarithm of 0 or negative
; % Program caused arithmetic error: Logarithm of 0 or negative
; 0.000000 0.000000 0.000000 0.000000 0.000000 0.301030
It seems to be, there are 'some differences' between SUN- and VAX-IDL.
Hope this helps.
Karl-Heinz.
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