# Setting up offsets array ...

• Subject: Setting up offsets array ...
• From: Peter Thorne <peter.thorne(at)uea.ac.uk>
• Date: Wed, 18 Apr 2001 15:10:33 +0100
• Newsgroups: comp.lang.idl-pvwave
• Organization: UEA, Norwich.
• Xref: news.doit.wisc.edu comp.lang.idl-pvwave:24600

```Dear all,

after your excellent help last time I thought that I would test the
waters again to see whether you can help me on my next problem. You'll
all get an acknowledgement in my thesis when (if?) I eventually finish
:-). This time I think the problem is really rather trivial I'm afraid
(famous last words?) - sorry.

The problem I now have is that I want to set up an offsets array to test
the sensitivity to the choice of histogram origin of the solution in my
last problem. Therefore, again one is working in space of unknown
dimensionality of between 1 and 5, which is known within the program
only upon call to it from a higher level program. What I want to be able
to do is set up an offsets array so that I can systematically shift the
origin over an entire space step in each dimension. For a 1-D problem
this is simple:

offsets=(findgen(11)*0.1)-0.5

Which can then be used to force the offset of the 1-D histogram around
the true origin by between -0.5 and 0.5 space units in the calling
program to JD's excellent hist_nd. The problem is how to generalise this
in the program to a potentially higher, and unknown (until call)
dimensional space. The number of combinations of shifts will be 11^n,
where n is the dimensionality of the histogram space. For a 2-D case the
offsets array will look like:

(-0.5,-0.5)
(-0.5,-0.4)
(-0.5,-0.3)
(-0.5,-0.2)
:
:
(-0.4,-0.5)
(-0.4,-0.4)
(-0.4,-0.3)
:
:
(0.5,0.5)

For each extra dimension another column would be added to the array and
the number of rows increased by *11. Therefore the offsets array will
always be fltarr(n,11^n) in size, it is the filling of this array with
the values that is causing me my latest headache :-(

Any ideas as to how to approach this problem will be very gratefully