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Need Math Instruction [message #83439]

Wed, 06 March 2013 17:22

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Folks,

I need some help with a math problem. Here are some values and an
expression. The result of the expression is a NaN.

arec= 7.0380332e-005
brec= 0.011374851
crec= 0.010008938
drec= 3.8378659e-005
Tprec = (brec-(brec^2 -4*arec)^(1.0/2))/(2*arec)

IDL> help, Tprec
TPREC FLOAT = -NaN

I want to know why this is a NaN and how to explain the following
results:

IDL> help, brec, arec
BREC FLOAT = 0.0113749
AREC FLOAT = 7.03803e-005

IDL> print, (brec^2 -4*arec)
-0.000152134
IDL> d = (brec^2 -4*arec)
IDL> help, d
D FLOAT = -0.000152134

IDL> print, d^(1.0/2)
-NaN

IDL> print, -0.000152134^(1.0/2)
-0.0123343

IDL> print, d, format='(F0.12)'
-0.000152134089

IDL> print, -0.000152134089D^(1.0/2)
-0.012334265

IDL> print, Float(-0.0001521340891486)^(1.0/2)
-NaN

IDL> print, -0.0001521340891486^(1.0/2)
-0.0123343

IDL> print, Double(-0.0001521340891486D)^(1.0/2)
-NaN

IDL> print, -0.0001521340891486D^(1.0/2)
-0.012334265

Any ideas?

Thanks,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")

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[Message index]

		Need Math Instruction By: David Fanning on Wed, 06 March 2013 17:22
		Re: Need Math Instruction By: DavidF[1] on Thu, 07 March 2013 15:34
		Re: Need Math Instruction By: Michael Galloy on Thu, 07 March 2013 15:31
		Re: Need Math Instruction By: DavidF[1] on Thu, 07 March 2013 14:41

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