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Re: IDL mathematics [message #2898 is a reply to message #2705]

Thu, 01 September 1994 05:13

sjt
Messages: 72
Registered: November 1993

Member

dean@phobos.cira.colostate.edu wrote:

: How come the following expression gives the wrong answer.

: J = 201+((1461*(1994+4799))/4)-(3*((1994+4899)/100)/4)-2465022

: J = -2457713

: It should be:

: J = 201+((1461.*(1994+4799.))/4.)-(3.*((1994+4899.)/100.)/4.)-24 65022.

: J = 16270.5

: Kelly Dean

The problem is IDL's conversion rules. You have two problems here:
a) 1461*(1994+4799) is a combination of 3 ints and is thus evaluated as
an int whereas it needs to be a long or float to get the right answer
b) Division of integers is an integer devide e.g. 3/2 = 1 and 4/5 = 0.

I think the minimal modification to get the right answer is:

J = 201+((1461.*(1994+4799))/4)-(3*((1994+4899)/100.)/4)-2465022
^ ^
--
James Tappin, School of Physics & Space Research
University of Birmingham
sjt@xun8.sr.bham.ac.uk
"If all else fails--read the instructions!"

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[Message index]

		IDL mathematics By: dean on Wed, 31 August 1994 10:49
		Re: IDL mathematics By: pjclinch on Fri, 02 September 1994 04:32
		Re: IDL mathematics By: sjt on Thu, 01 September 1994 05:13

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