%This fucction is called by mask1.m to optimiae the chi-square

function chi = chisq(x, smat, observed, fixdensity)

x = fixdensity .* x; %force zeros with fixdensity
model = x * smat;

%model = (fixdensity .* x) * smat ; %force zeros with fixdensity??

chi = sum ( ((observed - model) .^ 2) ./ abs(model) );

return;