| Re: Bug/feature in matrix multiply [message #14580] |
Fri, 12 March 1999 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Mark Fardal (fardal@weka.phast.umass.edu) writes:
> is the following a bug or feature? I don't understand why changing the
> type of the array changes the dimensions of the result. Then again,
> it's late on Friday, so my brain might just be mush.
>
> IDL> junk=fltarr(3)
> IDL> junk=reform(junk,3,1)
> IDL> help,junk
> JUNK FLOAT = Array[3, 1]
> IDL> help,[3.,2.,1.]#junk
> <Expression> FLOAT = Array[1]
> IDL> help,[3.d0,2.d0,1.d0]#junk
> <Expression> DOUBLE = Array[3, 3]
I don't know if it is a bug or a feature, but I
agree that it is strange. But so is this command:
junk = reform(junk, 3, 1)
Do you mean this:
junk = reform(junk, 1, 3)
The latter will make a column vector, which makes more
sense when multiplied by a row vector. What kind of result
were you expecting? From my reading of the # operator
I think the result with the floating array is correct.
I don't have a clue why the double expression does what
it does. :-(
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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