| Re: Yet again, The Sky is Falling! [message #52840] |
Fri, 09 March 2007 01:25  |
Paolo Grigis
Messages: 171
Registered: December 2003
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Senior Member |
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Here's a simple example of a routine that returns different
values if it is called by value or by reference.
pro pg,a,b
b=arg_present(a)
end
IDL> x=1
IDL> pg,x,b
IDL> print,b
1
IDL> pg,x+0,b
IDL> print,b
0
IDL> pg,x[0],b
IDL> print,b
0
Ciao,
Paolo
David Fanning wrote:
> yp writes:
>
>> You can download the code from www.research.plymouth.ac.uk/casix/temp/test_morel_LUT.pro
>>
>> You will also need the LUT (morel_fq.dat) to run the code.
>> www.research.plymouth.ac.uk/casix/temp/MOREL_FQ.DAT
>
> Well, I haven't tracked the actual culprit down yet, but
> the calculations in INT_LUT are doing *something* to the
> variables that are being passed in by reference. If I
> pass everything in by value, then there is no difference:
>
>
> IDL> int_LUT,412.5D, 1D, 0.0D, 0.0D, 0.0D, 0.03D, result3
> IDL> int_LUT,412.5D+0, 1D+0, nul+0, nul+0, nul+0, 0.03D+0, result4
> IDL> print,'RESULT 3: ', result3[*]
> IDL> print,'RESULT 4: ', result4[*]
>
> RESULT 3: 0.090100000 0.00000000 0.00000000
> 0.00000000 0.00000000 0.00000000 0.00000000
>
> RESULT 4: 0.090100000 0.00000000 0.00000000
> 0.00000000 0.00000000 0.00000000 0.00000000
>
> I suspect there is a calculation in there that sets one
> of the values very nearly to what you expect it to be,
> but not quite.
>
> Still weird, but more believable. :-)
>
> Cheers,
>
> David
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