function f = fitfunexp(lam, t, y)
%FITFUNEXP  Used  by PRCPRR to return errors in fitting data to a function.
%   FITFUNEXP is used by PRCPRR.  FITFUNEXP(lam,Data) returns the error
%   between the data and the values computed by the current
%   function of lam.  FITFUNEXP assumes a function of the form
%
%     y =  c(1)*exp(-lam(1)*t) + ... + c(n)*exp(-lam(n)*t)
%
%   with n linear parameters and n nonlinear parameters.

A = zeros(length(t),length(lam));
for j = 1:size(lam)
   A(:,j) = exp(-lam(j)*t);
end
c = A\y;
z = A*c;
f = z-y;