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From Phil Steitz <phil.ste...@gmail.com>
Subject Re: [math] RealLinearOperator and AbstractRealMatrix
Date Thu, 14 Jul 2011 15:39:02 GMT
On 7/14/11 3:49 AM, Gilles Sadowski wrote:
> On Wed, Jul 13, 2011 at 03:01:09PM -0700, Ted Dunning wrote:
>> Actually, this is a major issue.
> Indeed, it is an important design issue.
>
>> Take, for instance, the example of considering a Lucene index as a linear
>> operator.  The number of rows is the number of documents (which is changing
>> as documents are added) and the number of columns is the number of unique
>> terms (which is also changing as documents are added).
>>
>> Matrix multiplication consists of translating a (hopefully sparse) vector
>> into a query, running the query and interpreting the result as a (sparse)
>> vector.
>>
>> This is just one of a host of similar application oriented definitions of a
>> LinearOperator, none of which define the number of rows and columns at
>> construction time.
>>
>> I can still do a singular value decomposition of this linear operator
> Eventually it seems to come down to a programming style issue. What you
> expose above (the decomposition algorithm) uses _fixed_ dimensions; when you
> need another object (with different dimensions) you'll create a new one.

That is a serious constraint that you are proposing that we impose
at the top level of the hiearchy and force on all implementations. 
Ted's example indicates that in at least one potential practical use
case, this constraint would be problematic.   Reconstructing and
reestablishing state for what may be a complex object may not be
practical.  The decision that you are advocating is that all
supported linear operators and matrices must be immutable wrt
dimensions.  What happens when we try to implement an operator such
as Ted described?  Currently, we do not have that constraint, even
for matrices.  Why impose it on matrices now and extend it further
to linear operators?  Moreoever, why force all real matrices and
operators to maintain the (unecessary) fields in the superclass? 

Phil

>
> Both approaches are possible for your use case. But what I think should be
> avoided is several programming styles within a single library.
> The abstract accessor style is uncommon in CM and in the "linear" package,
> the implementations use this style for no good reason (as I've indicated in
> my previous mail).
>
>
> Regards,
> Gilles
>
>> On Wed, Jul 13, 2011 at 1:52 PM, Phil Steitz <phil.steitz@gmail.com> wrote:
>>
>>> This is not a huge issue, though, so I can live with it if you feel
>>> strongly that the fields should be persisted at the top level.
>>>
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