function resid=miss(x)
%This function returns the residual of the data from the model.  We pass in
%the data using the global variables:

global tpass cpass ceqpass

%We have the model concentrations:
c=x(1)+(x(2)-x(1))*exp(x(3)*tpass);

%And we have the residual:
resid=sum((c-cpass).^2)+(ceqpass-x(1))^2;

%Note that we have added in the residual due to the ceq measurement
%as well!  By the way, if some measurements were more accurate than
%others, the residual returned by this function should have each term
%weighted appropriately (by the inverse of the variance in each
%measurement).  This would improve the parameter estimation.