% Modified from (Lynch, 2004):
% Chapter 7 - Differential Equations.
% Program_7b - Solution curves, initial value problem.
% Copyright Birkhauser 2004. Stephen Lynch.

% Solve the differential equation and plot 2 solution curves.
clear all
% deqn1=inline('P(1)*(100-P(1))/1000','t','P');   % Define inline function
% [t,P1]=ode45(deqn1,[0 100],50);                 % Integrate differential equation (x_0 = 50)
% [t1,P2]=ode45(deqn1,[0 100],150);               % Integrate differential equation (x_0 = 150)
deqn1=inline('-0.1*P','t','P');   % Define inline function
[t,P1]=ode45(deqn1,[0 100],1);                 % Integrate differential equation (x_0 = 1)
[t1,P2]=ode45(deqn1,[0 100],-1);               % Integrate differential equation (x_0 = -1)

% ----- render x vs t graph  -----------
fsize=15;                       % set font size for graph
plot(t,P1(:,1), 'r')            % plot P(1) vs t, color red                     
hold on                         % retain the current plot to add more than 1 function
plot(t1,P2(:,1), 'b')           % plot P(1) vs t, color red 
hold off                        % release hold on current plot 
axis([0 100 -2 2])             % set axis
set(gca,'xtick',[0:20:100],'FontSize',fsize) % Set (Current axes handle) ticks, and fonts
set(gca,'ytick',[0:50:200],'FontSize',fsize) % Set (Current axes handle) ticks, and fonts
xlabel('t','FontSize',fsize)    % Set x-axis label
ylabel('P','FontSize',fsize)    % Set x-axis label

% End of Program_7b.