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Re: matrix division [message #60566 is a reply to message #60444]

Thu, 22 May 2008 09:19

Paul Van Delst[1]
Messages: 1157
Registered: April 2002

Senior Member

David Fanning wrote:
> jameskuyper@verizon.net writes:
>
>> For the integer case:
>>
>> ratio = numerator/denominator
>> bad = WHERE(denominator eq 0, count)
>> IF count gt 0 THEN ratio[bad] = replacement_value
>>
>> replacement_value needs to be carefully chose for the context of your
>> problem. You might want to give different replacement values depending
>> upon whether the numerator is positive, negative, or 0. There's
>> probably a more elegant approach, but three different WHERE's would
>> certainly be sufficient to cover those cases.
>>
>> For the floating point case, IDL fills in the relevant elements of
>> ratio with -Inf, Nan, or Inf, depending upon the sign of the
>> numerator, and I can't think of any better way of handling it than to
>> use precisely those value. If you need to use your result for further
>> computations where those values would be unacceptable, replace them,
>> with logic similar to the above, but using the FINITE() function.
>
> Shoot. I was hoping for an elegant solution. :-(

For something like this, the Fortran WHERE construct is teeny bit more elegant, e.g.

real, dimension(100,100) :: ratio, numerator, denominator
....
where (abs(denominator) > 0.0)
ratio = numerator/denominator
elsewhere
ratio = -999.9
end where

I like the fact that I don't have to explicitly use any indices indicated where good or
bad values are.

Anyway....

cheers,

paulv

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[Message index]

		matrix division By: adam.ranson on Wed, 21 May 2008 11:29
		Re: matrix division By: Kenneth P. Bowman on Fri, 23 May 2008 13:41
		Re: matrix division By: David Fanning on Fri, 23 May 2008 12:18
		Re: matrix division By: Vince Hradil on Fri, 23 May 2008 11:02
		Re: matrix division By: Jean H. on Fri, 23 May 2008 10:23
		Re: matrix division By: Vince Hradil on Fri, 23 May 2008 10:06
		Re: matrix division By: Jean H. on Fri, 23 May 2008 09:41
		Re: matrix division By: edward.s.meinel@aero. on Fri, 23 May 2008 08:13
		Re: matrix division By: adam.ranson on Fri, 23 May 2008 01:47
		Re: matrix division By: Kenneth P. Bowman on Thu, 22 May 2008 13:15
		Re: matrix division By: Jean H. on Thu, 22 May 2008 12:28
		Re: matrix division By: David Fanning on Thu, 22 May 2008 10:45
		Re: matrix division By: Rich Younger on Thu, 22 May 2008 10:22
		Re: matrix division By: Rich Younger on Thu, 22 May 2008 10:13
		Re: matrix division By: edward.s.meinel@aero. on Thu, 22 May 2008 09:47
		Re: matrix division By: Paul Van Delst[1] on Thu, 22 May 2008 09:19
		Re: matrix division By: David Fanning on Thu, 22 May 2008 08:48

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