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!pi: Stored as a float [message #28472]

Wed, 12 December 2001 12:22

Andy Loughe
Messages: 174
Registered: November 1995

Senior Member

Being stored as a float, the !pi system variable is accurate
to about the 6th decimal place.

IDL> print, !pi, format='(f25.23)'
3.14159274101257324218750

IDL> print, atan(1.0)*4.0, format='(f25.23)'
3.14159274101257324218750

IDL> print, size(!pi, /type) ;; 4 = Floating point
4

This would be better:

IDL> DEFSYSV, '!mypi', atan(1D)*4D, 1

IDL> print, size(!mypi, /type) ;; 5 = Double Precision
5

IDL> print, !mypi, format='(f25.23)'
3.14159265358979311599796
3.14159265358979323846264338327950288419716939937510 <- joyofpi.com

--
Andrew Loughe =====================================================
NOAA/OAR/FSL/AD R/FS5 | email: loughe@fsl.noaa.gov
325 Broadway | wwweb: www-ad.fsl.noaa.gov/users/loughe
Boulder, CO 80305-3328 | phone: 303-497-6211 fax: 303-497-6301

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