| Re: Try this [message #12946 is a reply to message #12945] |
Wed, 23 September 1998 00:00   |
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Joe[2]
Messages: 11
Registered: May 1998
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Junior Member |
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>
> In article <MPG.1071fa8a1e63e2a49896c8@news.frii.com>
> davidf@dfanning.com (David Fanning) writes:
>>
>> Ray Sterner (sterner@tesla.jhuapl.edu) writes:
>>
>>> Try this:
>>>
>>> x=dindgen(1000)/999.*20.
>>> for f=0.,10.,.02 do begin plot,/xstyl,x+f*1D6,sin(x) & empty & endfor
>>
>> Totally cool! :-)
>
> Weird yes, but definitively not cool for those who *want* to plot
> those data points!
>
> It took me a while to see what was going on here, but
> after running Ray's lines, do:
>
> plot,(x+1D7)(0:200),/xstyle,/ystyle,psym=3
>
> Now, a DOUBLE should have more dynamic range than to say that
> e.g., (x+1D7)(50) is *equal* to (x+1D7)(51). Luckily, it does:
>
> IDL> print,(x+1d7)([50,51]),form='(g20)'
> 10000001.00100100
> 10000001.02102102
>
> However, it appears that the PLOT command internally just works
> with FLOAT precision:
>
> IDL> print,FLOAT((x+1d7)([50,51])),form='(g20)'
> 1.000000e+07
> 1.000000e+07
>
> This could have been OK if some "zero point" value (typically the
> value of one of the tickmarks) had been subtracted in the process of
> converting to float. As it stands, this will have to be done
> by the user/programmer.
>
> Regards,
>
> Stein Vidar
But wouldn't they (RSI) have to go out of their way to purposefully
convert the doubles to float within plot in order for this to occur?
I would have thought that the double precision x-value would have
caused an inheritence cascade throughout the plot routine so that
everything would be double. Hmmmm... Oh wait, I got it! The
!x and !y structures are not double precision in their .range (and
other related) fields so it won't matter. This has to be done for
speed reasons since to make them double would force all plots
to use double precision calculations along with the attendant
decrease in computational rate. Still it is not obvious why they
need to force the x (and presumably y) variables to be float-type.
Z
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