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# emc-readme

README.txt — Plain Text, 4Kb

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==================================================== Release 0.5 of Electric Field Monte Carlo code (EMC) Dr. Min Xu <minxu@sci.ccny.cuny.edu> see COPYRIGHT ==================================================== 1. Pre-requirements EMC depends on the installation of certain softwares. (a) a C++ compiler GNU C++ should be fine. The compiler should support templates. (b) MIEV package by Dr. Warren J. Wiscombe (wiscombe@climate.gsfc.nasa.gov). This is an excellent code for Mie calculations. (c) mtwist-0.5 package by Prof. Geoff Kuenning at Harvey Mudd College (geoff@cs.hmc.edu). This is an Mersenne Twist Pseudorandom Number Generator Package. The Mersenne Twist method for generating pseudorandom numbers is an extremely fast, flexible, and desirable approach to random-number generation. It has superb statistical properties and a ridiculously long period (2^19937-1). (d) Netcdf package (optional) Netcdf API is used in some examples coming with EMC to store simulation outputs. The benefit of using netcdf files is the platform-independence of these files. I have included parts of (a-c) in the distribution only for the purpose your convenience. Full credit should be given to respective authors. 2. EMC EMC package is implemented in C++ and contained in three headers files. We use x as the size parameter of the particle, m the complex relative refractive index, S1 and S2 are the diagonal elements of the amplitude scattering matrix (whose off-diagonal elements are zero) in convention of Hulst. dmiev.h: a C interface for MIEV package, used by scatterer.h scatterer.h: a C++ header implementing a class "scatterer". The key methods include: // N and nslot can be increased for a higher accuracy // of the forward and inverse table. scatterer(double x, dcmplx m, int N=10001, int nslot=10000); // obtain S1 and S2 at a list of cosines of angles of // length n phasef(int n, double* mu, dcmplx* s1, dcmplx* s2); // obtain S1 and S2 at the cosine of one angle mu phasef(double mu, dcmplx* s1, dcmplx* s2); // a quicker version using the lookup table pre-computed phasef_lu(double mu, dcmplx* s1, dcmplx* s2); // yield the scattering angle given the probability // within (0,1) using the inverse table pre-computed draw_mu(double p); pol_montecarlo.h: the core header file of EMC implementing a class "photonPacket". The key methods include: // initialization photonPacket(const scatterer* sct, char* fname=NULL, unsigned long seed=0); // launch the photons. The incident electric field is // given by (E1, E2) where light is propagating in the // direction (u, v, w), E1 is in the direction (l, m, // n), and E2 is in the direction specified by the cross // product of the above two directions. Light is // incident upon the position (x,y,z) at time t. The // incident light intensity must be unity (|E1|^2 + // |E2|^2=1) and the directions must be unit vectors. void launch(dcmplx E1=1, dcmplx E2=0, double l=1, double m=0, double n=0, double u=0, double v=0, double w=1, double x=0, double y=0, double z=0, double t=0); // move to next scattering or absorption event void move(); // absorption event void absorb(); // scattering event void scatter(); // next event estimator of (Ed1, Ed2) with the // direction vector Q at time td crossing the boundary // z=zd in the direction (ud, vd, wd) void pointestimator(double *td, double *deposit, double Q[3][3], dcmplx *Ed1, dcmplx *Ed2, double zd, double ud=0, double vd=0, double wd=1); The photon status is stored in the public data members of the class, they are: xold, yold, zold, told: the position and time of the previous scattering event x, y, z, t, weight: the current position and time of photon and its weight E1, E2: electric field components P[3][3]: (l, m, n) the unit vector for E1 direction (p, q, r) the unit vector for E2 direction (u, v, w) the propagation direction nsct: number of scattering events