Regarding the Near-field Calculations

Regarding the Near-field Calculations

Pradeep Bhatia (guest) 02 Feb 2018 08:06

Dear Sir
I am doing the near-field calculations, as given in user guide of DDSCAT 7.3 on 29, 29.1 & 29.2 sections. when, we calculate the near-field calculation after choosing important parameter i.e. 1 = NRFLD (=0 to skip nearfield calc., =1 for nearfield E, =2 for E and B) and 2 = IORTH (=1 to do only pol. state e01; =2 to also do orth. pol. state), and 1 = IWRKSC (=0 to suppress, =1 to write ".sca" file for each target orient.; After doing these changing in ddscat.par file and run in the ddscat. we got the extra file like w000r000k000.E1 & w000r000k000.E2 and so on….w000r000k000.E200. Till now, i followed these steps.
Now, my Question is how to use .E2, .E2, .E3 and so on .E200 files for further calculation ?
Q1. Is it single point calculation.
Q2. If it is not single point calculation, then how to add these file into E1+E2…….=En
Q3. is it run directly through ddpostprocess or we have to make ddpostprocess.par file. if yes, then How to make and which parameter are use in ddpostprocess.par file. and how to run after preparing the ddpostprocess.par file.
I wish you will reply soon.
Thanking You

Re: Regarding the Near-field Calculations

draine 05 Feb 2018 21:31

As explained in the UserGuide, wxxxryyykzzz.E1 and wxxxryyykzzz.E2 each contain the electric fields
E_sca and E_inc at each point j in the computational volume, where the total E=E_sca+E_inc,
for incident polarizations 1 and 2.

The files wxxxryyykzzz.En are intended to be read by the program DDPOSTPROCESS.f90.
If you compile and run this on the same architecture that was used to run DDSCAT, DDPOSTPROCESS should be able to read the binary files wxxxryyykzzz.En created by DDSCAT.

Please see section 30 of the UserGuide for instructions on using DDPOSTPROCESS.
The user needs to create a file ddpostprocess.par to tell DDPOSTPROCESS what output is desired.
An example of ddpostprocess.par (as well as output files) can be found in examples_exp/ELLIPSOID_NEARFIELD

Shweta (guest) 05 Jun 2018 15:43

Sir, I am using DDSAT 7.3.2.
In ddpostprocess.par, the line
-0.59684 0.0 0.0 0.59684 0.0 0.0 501 = XA,YA,ZA, XB,YB,ZB (phys units), NAB
gives the electric field along one track.
I want to write electric field along a matrix (i.e. multiple tracks).
Please suggest the modification.

draine 05 Jun 2018 17:15

As explained in section 30.1 of the 7.3.2 UserGuide, each "track" is specified by one line in ddpostprocess.par
In principle, ddpostprocess.par can specify many tracks (one line per track).

If this doesn't address your requirements, then you may need to modify the program ddpostprocess.f90 to create a new version to write out what you want — see section 30.2 of the UserGuide for a few words about this. The critical piece of code is subroutine readnf.f90 (called by ddpostprocess.f90) which reads the stored data file (e.g., 'w000r000k000.E1') from disk, and returns information about the polarization, electric field, etc at each lattice site. You will probably need prior experience with f90 programming if you are going to undertake this route.

It would be nice if some DDSCAT user would write some MATLAB code to do this, and make it available, but so far as I am aware this hasn't happened.