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add missing volume member to dft_energy class and Scheme example for computing group velocity #753

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Mar 6, 2019
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add missing volume member to dft_energy class and Scheme example for computing group velocity #753

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f7b67d9
add volume to dft_energy
oskooi Feb 28, 2019
cef4dfd
add example demonstrating equivalence of computing group velocity usi…
oskooi Mar 4, 2019
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37 changes: 37 additions & 0 deletions scheme/examples/group-velocity.ctl
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Original file line number Diff line number Diff line change
@@ -0,0 +1,37 @@
;; compute group velocity of a waveguide mode using two different methods
;; (1) ratio of Poynting flux to energy density
;; (2) via MPB from get-eigenmode-coefficients

(set-param! resolution 20)

(set! geometry-lattice (make lattice (size 10 5 no-size)))

(set! geometry (list (make block
(center 0 0 0)
(size infinity 1 infinity)
(material (make medium (epsilon 12))))))

(set! pml-layers (list (make pml (thickness 1))))

(define-param fsrc 0.15)

(set! sources (list (make eigenmode-source
(src (make gaussian-src (frequency fsrc) (fwidth (* 0.2 fsrc))))
(center -3 0 0)
(size 0 5 0)
(eig-band 1)
(eig-parity (+ ODD-Z EVEN-Y))
(eig-match-freq? true))))

(define flux (add-flux fsrc 0 1 (make flux-region (center 3 0 0) (size 0 5 0))))
(define energy (add-energy fsrc 0 1 (make energy-region (center 3 0 0) (size 0 5 0))))
(run-sources+ 100)

(define res (get-eigenmode-coefficients flux (list 1) #:eig-parity (+ ODD-Z EVEN-Y)))
(define mode-vg (array-ref (list-ref res 1) 0 0))

(define poynting-flux (list-ref (get-fluxes flux) 0))
(define e-energy (list-ref (get-electric-energy energy) 0))
(define ratio-vg (/ (* 0.5 poynting-flux) e-energy))

(print "group-velocity:, " ratio-vg ", " mode-vg "\n")
53 changes: 29 additions & 24 deletions src/dft.cpp
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Expand Up @@ -446,29 +446,32 @@ dft_flux fields::add_dft_flux(const volume_list *where_, double freq_min, double

dft_energy::dft_energy(dft_chunk *E_, dft_chunk *H_,
dft_chunk *D_, dft_chunk *B_,
double fmin, double fmax, int Nf)
{
double fmin, double fmax, int Nf, const volume &where_)
: Nfreq(Nf), E(E_), H(H_), D(D_), B(B_), where(where_) {
if (Nf <= 1) fmin = fmax = (fmin + fmax) * 0.5;
freq_min = fmin;
Nfreq = Nf;
dfreq = Nf <= 1 ? 0.0 : (fmax - fmin) / (Nf - 1);
E = E_; H = H_; D = D_; B = B_;
}

dft_energy::dft_energy(const dft_energy &f) {
freq_min = f.freq_min; Nfreq = f.Nfreq; dfreq = f.dfreq;
E = f.E; H = f.H; D = f.D; B = f.B;
dft_energy::dft_energy(const dft_energy &f) : where(f.where) {
freq_min = f.freq_min;
Nfreq = f.Nfreq;
dfreq = f.dfreq;
E = f.E;
H = f.H;
D = f.D;
B = f.B;
}

double *dft_energy::electric() {
double *F = new double[Nfreq];
for (int i = 0; i < Nfreq; ++i) F[i] = 0;
for (int i = 0; i < Nfreq; ++i)
F[i] = 0;
for (dft_chunk *curE = E, *curD = D; curE && curD;
curE = curE->next_in_dft, curD = curD->next_in_dft)
for (size_t k = 0; k < curE->N; ++k)
for (int i = 0; i < Nfreq; ++i)
F[i] += 0.5*real(conj(curE->dft[k*Nfreq + i])
* curD->dft[k*Nfreq + i]);
F[i] += 0.5*real(conj(curE->dft[k * Nfreq + i]) * curD->dft[k * Nfreq + i]);
double *Fsum = new double[Nfreq];
sum_to_all(F, Fsum, Nfreq);
delete[] F;
Expand All @@ -477,13 +480,13 @@ double *dft_energy::electric() {

double *dft_energy::magnetic() {
double *F = new double[Nfreq];
for (int i = 0; i < Nfreq; ++i) F[i] = 0;
for (int i = 0; i < Nfreq; ++i)
F[i] = 0;
for (dft_chunk *curH = H, *curB = B; curH && curB;
curH = curH->next_in_dft, curB = curB->next_in_dft)
for (size_t k = 0; k < curH->N; ++k)
for (int i = 0; i < Nfreq; ++i)
F[i] += 0.5*real(conj(curH->dft[k*Nfreq + i])
* curB->dft[k*Nfreq + i]);
F[i] += 0.5*real(conj(curH->dft[k * Nfreq + i]) * curB->dft[k * Nfreq + i]);
double *Fsum = new double[Nfreq];
sum_to_all(F, Fsum, Nfreq);
delete[] F;
Expand All @@ -494,33 +497,35 @@ double *dft_energy::total() {
double *Fe = electric();
double *Fm = magnetic();
double *F = new double[Nfreq];
for (int i = 0; i < Nfreq; ++i) F[i] = Fe[i]+Fm[i];
for (int i = 0; i < Nfreq; ++i)
F[i] = Fe[i]+Fm[i];
delete[] Fe;
delete[] Fm;
return F;
}

dft_energy fields::add_dft_energy(const volume_list *where_,
double freq_min, double freq_max, int Nfreq) {

if (!where_) // handle empty list of volumes
return dft_energy(NULL, NULL, NULL, NULL, freq_min, freq_max, Nfreq, v);

dft_chunk *E = 0, *D = 0, *H = 0, *B = 0;
volume_list *where = S.reduce(where_);
volume firstvol(where_->v);
volume_list *where = new volume_list(where_);
volume_list *where_save = where;
while (where) {
LOOP_OVER_FIELD_DIRECTIONS(gv.dim, d) {
E = add_dft(direction_component(Ex, d), where->v, freq_min, freq_max, Nfreq,
true, 1.0, E);
D = add_dft(direction_component(Dx, d), where->v, freq_min, freq_max, Nfreq,
true, 1.0, D);
H = add_dft(direction_component(Hx, d), where->v, freq_min, freq_max, Nfreq,
true, 1.0, H);
B = add_dft(direction_component(Bx, d), where->v, freq_min, freq_max, Nfreq,
true, 1.0, B);
E = add_dft(direction_component(Ex, d), where->v, freq_min, freq_max, Nfreq, true, 1.0, E);
D = add_dft(direction_component(Dx, d), where->v, freq_min, freq_max, Nfreq, false, 1.0, D);
H = add_dft(direction_component(Hx, d), where->v, freq_min, freq_max, Nfreq, true, 1.0, H);
B = add_dft(direction_component(Bx, d), where->v, freq_min, freq_max, Nfreq, false, 1.0, B);
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The change to pass false for two of the fields is what is fixing your dV factor. Adding the where field to dft_energy is unrelated (and is actually unused in this PR).

}
where = where->next;
}
delete where_save;

return dft_energy(E, H, D, B, freq_min, freq_max, Nfreq);
return dft_energy(E, H, D, B, freq_min, freq_max, Nfreq, firstvol);
}

void dft_energy::save_hdf5(h5file *file, const char *dprefix) {
Expand Down
3 changes: 2 additions & 1 deletion src/meep.hpp
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Expand Up @@ -1053,7 +1053,7 @@ class dft_flux {
class dft_energy {
public:
dft_energy(dft_chunk *E_, dft_chunk *H_, dft_chunk *D_, dft_chunk *B_,
double fmin, double fmax, int Nf);
double fmin, double fmax, int Nf, const volume &where_);
dft_energy(const dft_energy &f);

double *electric();
Expand Down Expand Up @@ -1082,6 +1082,7 @@ class dft_energy {
double freq_min, dfreq;
int Nfreq;
dft_chunk *E, *H, *D, *B;
volume where;
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This needed only if you add an fields::output_dft method for dft_energy.

};

// stress.cpp (normally created with fields::add_dft_force)
Expand Down