[Nexus] NeXus Digest, Vol 58, Issue 5

[Brian Tieman]

On 4/19/2010 7:51 AM, Mark Koennecke wrote:
> Dear Brian Pauw,
>
> Brian Pauw wrote:
>> Dear Freddie,
>>
>> The timescale I was thinking of was on the order of within several 
>> months. Would this be feasible? I am looking into the HDF file format 
>> option at the moment. The key issue is not just reading but reading 
>> _and_ writing (as I don't have nexus files yet and no way to generate 
>> them).
>>
>> Yours sincerely,
>>
>>
> In an idle moment I looked at the matlab documentation for a bit, 
> especially the external interface.
> I realized that matlab can use external Java classes. If this really 
> works (I have no time now to test
> this) then you may use the existing NeXus-Java binding. It will 
> require some conversion from matlab
> to Java arrays but I would not be surprised if a utility function for 
> doing this exists somewhere.
> A conversion would anyway be required as NeXus uses C-storage order 
> whereas matlab uses
> Fortran storage order.
>

I use Matlab to call java classes.  It works really well.  Matlab has a 
classpath.txt file that one needs to modify to add in the new jar 
files.  Once they are added in, one can create a Matlab "class" with a 
command like:

     client = gov.anl.aps.tieman.mpicorrelator.client.matlab.MatlabClient ()

A call to

     methods (client)

will then return all the methods in the java class 
gov.anl.aps.tieman.mpicorrelator.client.matlab.MatlabClient ().  The 
methods can be easily called from Matlab.  For example, the method

     public int[][] getDynamicPartitionMap(String libraryPath, String 
mapName)

can be called from Matlab with the call

     dynamicPartitionMap = client.getDynamicPartitionMap 
(partitionMapLibraryPath, partitionMapFiles(3));

Mark is right, the arrays are fortran ordered in Matlab so may need to 
be flipped somewhere.  You also need to be mindful of the data types as 
Java is a strongly typed language.

I'm calling java from Matlab to open Nexus files in a round-a-bout sort 
of way.  Matlab is calling java classes that wrapper service calls to 
Jax_WS services on a server.  It is the Jax-WS services that are opening 
the nexus files.  Certainly if Matlab can't interface to the Java HDF 
routines directly--or you wish to flip the dims or do some other 
activities outside of Matlab--writing a java wrapper for Matlab to call 
instead is feasible.

Brian

> Best Regards,
>
>           Mark Koennecke
>
>> Brian.
>>
>> On 15 Apr 2010, at 20:00, nexus-request at nexusformat.org wrote:
>>
>>> What sort of timescale were you looking at to start using NeXus
>>> files?
>>
>> Yours sincerely,
>>
>>
>> Brian R. Pauw.
>
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