[Nexus] large Nexus files

[Peterson, Peter F.]

Branton,

The way to do this is by creating the SDS (NXmakedata), then making
several calls to NXputslab which don't need to be in any order.
Remember, a single number is a "rectangular slab", however inefficient.
The assumption made is that you know the total size of the SDS upon
starting.

P^2

-----Original Message-----
From: nexus-bounces at anl.gov [mailto:nexus-bounces at anl.gov] On Behalf Of
Campbell, Branton
Sent: Monday, July 17, 2006 10:34 PM
To: nexus at anl.gov
Subject: [Nexus] large Nexus files

Dear Nexus users,

Suppose that I have a large (much bigger than computer memory) 3D array
that I must create and write to a single Nexus dataset.  Also assume
that I must compute the array values in an apparently random order.
Have the Nexus developers envisioned an efficient way to use the Nexus
API routines to write these elements in random order (i.e. not in nice
rectangular slabs)?  In the past, I have used direct-access files for
this purpose.

Of course, I would be better off sticking to arrays that fit in memory.
But I envision situations where this will not be possible (thousands of
8MB images used to reconstruct large contiguous volumes of reciprocal
space), and where it will be very expensive to break the output array up
into slabs and calculate them one at a time.

Best wishes,
Branton

****************************************
Branton J. Campbell
Department of Physics & Astronomy
Brigham Young University
N261 ESC, BYU, Provo, UT 84602
Tel: 801-422-5758 Fax: 801-422-0553
Email: branton_campbell at byu.edu
http://www.physics.byu.edu/faculty/campbell/


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