| Re: SIGN function? [message #6055] |
Wed, 03 April 1996 00:00 |
agraps
Messages: 35
Registered: September 1994
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Member |
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llobet@elpp1.epfl.ch (Xavier Llobet i Sales EPFL-CRPP 1015 Lausanne CH) writes:
> Maybe today I am specially dumb, but I cannot find the IDL (version 3.6.1)
> function that gives the sign of a number (I suppose it exists!!!).
I don't know. I wrote my own, attached below. It works for a number
of cases, but there are no guarantees.
Amara
-----------------------
function SIGN, num
;+
;NAME:
; SIGN
;
;PURPOSE:
; To compute the sign of a number. This function mimics
; Matlab's sign function.
;
;CALLING SEQUENCE:
; Result = SIGN(num)
;
;INPUTS:
; Num: Any number or array
;
;OUTPUTS:
; SIGN returns either 1, 0, or -1.
;
;MODIFICATION HISTORY:
; Amara Graps, BAER, December 1994.
; (c) copyright Amara Graps 1995, 1996.
;-
t = SIZE(num)
testtype = t(0)
IF testtype NE 0 THEN BEGIN
;The value num is an array.. Find the sign of ALL of the elements
;create same size and kind of array
n_ele = N_ELEMENTS(t)
CASE t(n_ele-2) OF
2: sgn = num * 0 ;integer
3: sgn = num * 0L ;long integer
4: sgn = num * 0.0 ;floating
5: sgn = num * 0.0D0 ;double floating
ELSE: print, 'Not a good array type in sign!'
ENDCASE
copy_num= num
;neg values
indx = WHERE(copy_num LT 0)
;check for bad index
ts = SIZE(indx)
CASE 1 OF
ts(0) EQ 0: ;no change
ELSE: sgn(indx) = -1
ENDCASE
;positive values
indx = WHERE(copy_num GT 0)
;check for bad index
ts = SIZE(indx)
CASE 1 OF
ts(0) EQ 0: ;no change
ELSE: sgn(indx) = +1
ENDCASE
;zero values
indx = WHERE(copy_num EQ 0)
;check for bad index
ts = SIZE(indx)
CASE 1 OF
ts(0) EQ 0: ;no change
ELSE: sgn(indx) = 0
ENDCASE
ENDIF ELSE BEGIN
;t(0) = 0, scalar.. what we want
IF t(1) NE 6L then begin
;Not a complex scalar
CASE 1 OF
num LT 0: sgn = -1
num EQ 0: sgn = 0
num GT 0: sgn = 1
ELSE: print, 'Not a valid number!'
ENDCASE
ENDIF ELSE BEGIN
;This is a complex scalar
sgn = num / abs(num)
END ;END
END
RETURN, sgn
END
--
************************************************************ *************
Amara Graps email: agraps@netcom.com
Computational Physics vita: finger agraps@best.com
Multiplex Answers URL: http://www.amara.com/
************************************************************ *************
"Picture a massless particle." --A Koan of Modern Physics
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