function cost=ecopz_costfxn(pin)
% Toy 2-box ecosystem model
%

% define "global" paprameters and assign values
global MLD p tobs xobs

p=pin;

T=[0:5:100]';      % use a fixed time-scale to compare obs.
n=length(T);

X0=[0.1 0.1]';

[T,X]=ode15s('ecopz',T,X0);

cost = sum((xobs(:,1)-X(:,1)).^2 + (xobs(:,2)-X(:,2)).^2)