%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%initialize differential equation, initial conditions
% and constants needed for other functions
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%initialize differential equation
global A;
A=[ 0 -1;1 0]    % defines matrix of the differential equation

%initialization for integration.m with ode23
x0 = [8 4]'      % Define initial conditions.
t0 = 0;          %initial time for integration
tfinal = 15;     %final time for integration
tfinal = tfinal*(1+eps);
deltat=0.1;        %time step
tol = 1.e-3;     % Accuracy of integration
trace = 1;       %output intermediate results 

%initialization for quiver.m
arrowlength=1.5;
xmax=10;
xmin=-xmax;
ymax=10;
ymin=-ymax;
gridsizex=1;
gridsizey=gridsizex;

%clear plot
clf