Fwd: Re: JAMA Improvement: Double JAMA's Speed

[boisvert@nist.gov]

----- Forwarded message from Anders Peterson <anders_peterson@optimatika.se> -----
    Date: Mon, 12 Nov 2007 16:47:34 +0100
    From: Anders Peterson <anders_peterson@optimatika.se>
Reply-To: Anders Peterson <anders_peterson@optimatika.se>
 Subject: Re: JAMA Improvement: Double JAMA's Speed
      To: jama@nist.gov

I now think that the reason ojAlgo seems to perform slower with small 
matrices in spite of its monolithic array design is a different aspect 
of the array design. To modify ojAlgo dense/physical matrices you 
typically call a method like this:


    protected void modifyAll(UnaryFunction<Double> aFunc) {
        for (int i = 0; i < myArray.length; i++) {
            myArray[i] = aFunc.invoke(myArray[i]);
        }
    }


For small matrices that design is not efficient, but for larger matrices 
it is very efficient.

I've long thought about doing specific implementations for small, fixed 
size, matrices. The 3x3 case is obvious, but I don't really know what 
else would be needed. (I'm not a graphics programmer.)

/Anders
http://ojalgo.org/


Joe Hicklin wrote:
> Why just for small matrices?
>
>
> -----Original Message-----
>   
>> From: jama@nist.gov [mailto:jama@nist.gov] On Behalf Of
>>     
> boisvert@nist.gov
> Sent: Sunday, November 11, 2007 5:27 PM
> To: Multiple recipients of list
> Subject: Fwd: JAMA Improvement: Double JAMA's Speed
>
>
>
> ----- Forwarded message from "Castro, Giovanny A"
> <> -----
>     Date: Fri, 9 Nov 2007 20:26:04 -0500
>     From: "Castro, Giovanny A" <>
>  Subject: JAMA Improvement: Double JAMA's Speed
>       To: boisvert@nist.gov
>
>
> JAMA Authors, 
>
>
> I have a somewhat strange but valid proposal to improve the JAMA
> library:
>
> There should be a Matrix subclass for Matrix sizes under 15.
> Why? To take advantage of dramatic performance increases when using 
> one dimensional arrays at these sizes.
>
> For a 4x4 matrix a one dimensional array implementation is TWICE as fast
> as the JAMA implementation. 
>
> Why are 4x4 and 3x3 matrices important? They are critical to computer
> graphics and engineering applications. It would be my guess that a large
> percentage of people interested in a matrix library are interested in 
> using it in a computer graphics application - or in other engineering
> applications requiring scaling, translation and rotation.
>
> As it stands, JAMA is completely unacceptable for these applications.
>
> Especially in computer graphics applications, Java developers are
> already at a disadvantage compared to C/C++ (even Flash) developers. 
>
> If they could DOUBLE their Matrix and Vector multiplication (rotation)
> performance why would they choose JAMA?
>
> Unfortunately, implementing this proposal would require a redesigning of
> the JAMA library which is why I know this is a strange proposal.
>
> Developers cant subclass the Matrix class to do this themselves because
> it contains the double A[][] variable. Matrix might have to be an 
> abstract class with subclasses defining the data storage. There might 
> have to be a factory method by which to create matrices because
> it would have to return a one-dimensionally or two-dimensionally backed
> matrix depending on the dimensions...
>
> Obviously, I haven't considered the specifics of what would have to be
> done to JAMA to achieve this but I hope ive piqued someone curiosity 
> on this subject.  
>
> This thread is extremely chaotic but by the end the disparity between
> one-dimensional and two-dimensional arrays is shown:
>
> http://forum.java.sun.com/thread.jspa?threadID=5234721&tstart=0
>
> These are the results of JAMA vs a one-dimensional implementation doing 
> 2 million matrix multiplication operations on 4x4 matrices (in
> milliseconds):
>
> One Dim Time: 3626
> JAMA Time: 7625
>
> One Dim Time: 3438
> JAMA Time: 7610
>
> One Dim Time: 3235
> JAMA Time: 7516 
>
> One Dim Time: 3235
> JAMA Time: 7532
>
> One Dim Time: 3250
> JAMA Time: 7610
>  
>
> Giovanny Castro
>
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