Possible bin-center/edge issue with sw_plotspec

[RichardWaiteSTFC]

To Reproduce:

(1) Run this script with 11 q-bins in call to spinwave and plot using sw_plotspec

nqbins = 11  % <- CHANGE THIS IN STEP 2
dE = 0.1 % <- CHANGE THIS IN STEP 3
FMchain = spinw;
FMchain.genlattice('lat_const',[3 8 8],'angled',[90 90 90],'spgr',0);
FMchain.addatom('r',[0 0 0],'S',1,'label','MCu1','color','blue');
FMchain.gencoupling('maxDistance',7)
FMchain.addmatrix('value',-eye(3),'label','Ja','color','green')
FMchain.addcoupling('mat','Ja','bond',1);
FMchain.genmagstr('mode','direct', 'k',[0 0 0],'n',[1 0 0],'S',[0; 1; 0]);
FMspec = FMchain.spinwave({[0 0 0] [1 0 0], nqbins},'hermit',false);
FMspec = sw_egrid(FMspec,'component','Sperp', 'Evect', 0:dE:6);
sw_plotspec(FMspec)

(2) Run the script again with nqbins=21
It looks like the patches are no longer at the bin center in q

(3) Change the energy binning dE=0.15 - this looks like it fixes the problem

Perhaps it matters whether the energy bin edges coincide with the eigenvalues? Not sure why though. Also the colorfill plotting (inside sw_plotspec) is done by the image function which does apparently center the patch on the bin center (unlike some colorfill plotting functions which put the bottom left corner of the patch at the bin center).