Re: [eigen] Multi Dimensional Arrays

[Jim Bosch <talljimbo@xxxxxxxxx>]

On 02/08/2011 05:13 PM, Andy Somogyi wrote:
> From what I understand, the only way to handle multi dimensional
> arrays with Eigen is something along the lines of
>
> Array<Array<double,Dynamic,Dynamic>  ,Dynamic, Dynamic>  ...
>
> This is really far from ideal as it really is an array of arrays
> (separate memory blocks).  Has there been any talk of merging in some
> multi dimensional support to Array, say from the now defunct blitz++
> code, or adding it a new?

That's not entirely true; while Eigen is limited to 2 dimensions,
Eigen::Matrix is not an array of arrays - they're allocated as a single
memory block.

> I really really really just want to use A SINGLE LIBRARY, and have to
> rely on Eigen for linear algebra, and boost multi-array or blitz++
> for multi-dimensional arrays. What would be nice is to have a
> multi-dim array, be able to grab a dimension or sub-array out of it,
> and use it directly as an Eigen Array / Matrix.

I feel your pain, and I've been working on a multidimensional array 
library that's designed to let Eigen do all the matrix math:

http://code.google.com/p/ndarray/

While that isn't the complete solution solution you're looking for, at 
least it's a clear division of labor.

Essentially, while you can make an ndarray::Array of any dimension, you 
can view 1- or 2-dimensional subarrays of those as Eigen-conforming 
objects, or construct ndarray views into Eigen::Matrix objects.

That won't get you all the way there if your main application is 
multidimensional tensor contractions, but it does provide a nice 
interface for interfacing with Python/Numpy and moving Eigen-compatible 
objects around with reference counting instead of deep copies.

Good Luck!

Jim Bosch