In order to combine the three graphs in a unique figure you could use subplot.
figure
% First set of data
subplot(1,3,1)
plot(x_graph1, y_graph1, 'color', 'b')
title('Data of code 1')
% Second set of data
subplot(1,3,2)
plot(x_graph2, y_graph2, 'color', 'r')
title('Data of code 2')
% Third set of data
subplot(1,3,3)
plot(x_graph3, y_graph3, 'color', 'g')
title('Data of code 3')
Or if you just want the three data sets in a unique graph you could just:
figure
plot(x_graph1, y_graph1, 'color', 'b')
hold on
plot(x_graph2, y_graph2, 'color', 'r')
hold on
plot(x_graph3, y_graph3, 'color', 'g')
