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From Sébastien Brisard <>
Subject Re: [math] Transposable linear operators
Date Thu, 12 Jan 2012 14:16:53 GMT
2012/1/12 Ted Dunning <>:
> One such example is a text retrieval engine.  A x is easy since that is
> what the engine does.  A' y is very expensive.
> 2012/1/12 Sébastien Brisard <>
>> In other words, I do not know how to access
>> efficiently the (i, j) coefficient, but I *do* know how to compute
>> efficiently A.x. There might be some cases where computing A'.x would
>> still be difficult. I do not have an example here, but that's the
>> reason why initially
>> RealVector operateTranspose(RealVector)
>> was not put in the RealLinearOperator abstract class.

Thanks for this example! So you *do* agree that implementing
operateTranspose() should be optional, don't you?

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