| Re: BVLS (NNLS) without loops? [message #86962 is a reply to message #86953] |
Tue, 17 December 2013 09:35   |
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Mike[5]
Messages: 5
Registered: October 2013
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Junior Member |
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Hi Juan Pablo,
From what I understand, your BVLS (Bounded-Variables Least-Squares) problems in every pixel are completely independent. They don't share the coefficients of the A array nor the B vector. The only similarity between the different problems is the size of the arrays.
If this is the case I don't see how one could speed-up the problem by some form of vectorization.
The only real solution would be for IDL to include a compiled BVLS routine in the core language. I had hoped for this to happen for some time, given that so much spectral analysis work has to solve this kind of problem.
So I take the opportunity of your message to suggest to Exelis to consider the inclusion of a compiled version of BVLS (http://www.netlib.org/lawson-hanson/all) in the core language.
Cheers,
Michele
On Tuesday, December 17, 2013 6:32:00 AM UTC, JP wrote:
> Hi IDLers,
>
> I am currently using BVLS (http://www-astro.physics.ox.ac.uk/~mxc/idl/bvls.pro) for spectral unmixing. It works great, but, on one pixel at a time. I want to implement for many pixels without having to loop. Example below:
>
>
>
> IDL> help, a
>
> A FLOAT = Array[85, 3]
>
> IDL> help, b
>
> B FLOAT = Array[85]
>
> IDL> help, bnd
>
> BND FLOAT = Array[2, 3]
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> IDL> print, bnd
>
> 0.000000 1.00000
>
> 0.000000 1.00000
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> 0.000000 1.00000
>
>
>
>
>
> bvls, A, B, BND, X_BVLS
>
>
>
> IDL> help, x_bvls
>
> X_BVLS FLOAT = Array[3]
>
>
>
> in my example A is a vector of "endmembers" (85 spectral bands and 3 fractions), B is a pixel (vector of 85 bands), BND are bounds (don't go negative nor >1) and the X_BVLS are the estimated fractions returned for that pixel.
>
> Now as you could imagine I have many many pixels (n) (my B is really a 2D array of [85, n]) and i've written a function which loops through n, but it gets very slow for large n.
>
>
>
> Any ideas?
>
>
>
> Thanks
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