Hi Suman Dhayaj

We have Implemented FFT near-field. One version of this paper is available here:

ftp://ftp.astro.princeton.edu/draine/papers/pdf/OptEx_20_1247.pdf

But if you download DDSCAT code from

http://www.ddscat.com

you can also look at our implementation. It uses FFT but if do not have many dipoles you can calculate

near field witout FFT technique. We had a simple version of the near field calculation available in the

DDSCAT release before the 2012 (we can point to it if you need).

It is difficult for us to study your implementation because of time constraints on our part.

Piotr

On Fri, Nov 18, 2016 at 11:45 AM, Suman Dhayal <moc.liamg|layahdss#moc.liamg|layahdss> wrote:

Dear Professor Draine, Flatau,

This is Ms Suman Dhayal, an associate in research at Duke University. I need some help with the calculations using discrete-dipole approximation.

I have written the codes for calculations using DDA following the description in your JOSA, 11, 1994 paper. I have used it to do some Raman scattering calculations, and I am interested in doing some near field calculations now. I looked through your codes user's guide and some other papers but perhaps I am missing some information. If you could help me with it, I will be grateful to you.

So my query is over whether it will be correct to just take the unknown polarizations obtained by solving the simultaneous equations (7) from your paper and plug them in the general dipole field formula to compute the field in and around a sphere containing a cluster of spheres? I am attaching the small program I have written to do this if you would like to have a look at it.

It will be a big help if you could say whether I am doing it correctly. If not, some suggestion over where I am going wrong and how I may be able to correct it.

Thank you so much for your help,

Suman

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