%% %%%%%% MATLAB ODE Simulation of the Budding Yeast Cell Cycle %%%%%% %%
% The ODE model is taken from Chen(2004): 
% Chen, K.C. and Calzone, L. and Csikasz-Nagy, A. and Cross, F.R. and
% Novak, B. and Tyson, J.J. 2004. Integrative analysis of cell cycle 
% control in budding yeast, Molecular Biology of the Cell 15:3841-3862
% The equations and parameters were downloaded from
% http://mpf.biol.vt.edu/research/budding_yeast_model/model_download/bychen04.ode
% and converted into MATLAB code by Kartik Subramanian (VirginiaTech) and
% Kamaludin Dingle (Oxford Univ.). September 2010.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%% event_yeast.m %%
% This file contains the reset rules (Chen(2004) page 3845) for the cell
% cycle.
function [value,isterminal,direction] = event_yeast(t,y)
% This calls the function (variable name) so that the variables are
% recognized by their name rather than y(1), y(2)...- see comments 
% in function for details
variable_name; 

% Two of the parameters which are needed here
KEZ=0.3;
kez2=0.2;

% Locate the time when values passes through zero in a 
% increasing direction and stop integration.
value=[sign(y(nCLB2) - KEZ); sign(y(nCLB2)+y(nCLB5)-kez2); sign(y(nORI)-1);sign(y(nSPN)-1)]; 
isterminal=[1; 1; 1; 1];  % 1 indicates that solver stops when event is reached
direction=[-1; -1; +1; +1]; % -1 means event takes place when the trigger point is crossed from lower to 
                            %    higher value; +1 means event takes place when trigger point is crossed from higher to lower value