%
% program to solve the ODE
%
%  dy/dt = exp(-a*y^2)
%

clear        % if you use the clear command after the global declaration
             % it clears the global
global a

y0=input(' enter initial value of y: ');
a=input(' enter value of a: ');
tfinal=input(' enter final time: ');

t0=0;
tstep=(tfinal-t0)/100;
tspan=0:tstep:tfinal;

% note that although by we have specified a range of
% t values at which the result is required (tspan)
% the routine still calculates the solution on a variable
% time grid, as required for high accuracy and efficiency
%

[t,y]=ode45('simple_rhs', tspan, y0);

plot(t,y)
title('solution of dy/dt=exp(-a*y^2)');
xlabel('time(t)');