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Re: -0.0 [message #74533]

Fri, 21 January 2011 16:13

kisCA
Messages: 78
Registered: January 2011

Member

On Jan 20, 2:29 pm, Paolo <pgri...@gmail.com> wrote:
> On Jan 20, 2:22 pm, kisCA <ki...@hotmail.com> wrote:
>
>> I like this "sky is falling" things :-)
>
>> I guess that it could be a problem of precision with float...the range
>> should be higher in positive value in order to have 0 on the positive
>> side?
>
>> Thanks!
>
> Well yes. What happens is that when you do
>
> plot,[0,0],xrange=[-0.6,0.6],xtickv=vvv
>
> is that the plot range is given by
>
> r=!X.crange
>
> print,r,format='(f13.10)'
> -0.6000000238
> 0.5999999762
>
> IDL presumably uses the following formula to create 7 tick marks:
>
> tickv=r[0]+(r[1]-r[0])/6.0*findgen(7)
>
> print,tickv,format='(f13.10)'
> -0.6000000238
> -0.4000000238
> -0.2000000238
> -0.0000000238
> 0.1999999762
> 0.3999999762
> 0.5999999762
>
> When rounded to something more useful for plots:
>
> print,tickv,format='(f4.1)'
> -0.6
> -0.4
> -0.2
> -0.0
> 0.2
> 0.4
> 0.6
>
> That's how you get the negative zero.
>
> Ciao,
> Paolo

Well demonstrated. Thanks for the teaching!

Cheers

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[Message index]

		Re: -0.0 By: kisCA on Fri, 21 January 2011 16:13
		Re: -0.0 By: pgrigis on Thu, 20 January 2011 14:29
		Re: -0.0 By: kisCA on Thu, 20 January 2011 11:26
		Re: -0.0 By: kisCA on Thu, 20 January 2011 11:22
		Re: -0.0 By: David Fanning on Thu, 20 January 2011 11:16
		Re: -0.0 By: pgrigis on Thu, 20 January 2011 11:11

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