
[t,c] = ode45(@odefun1,[0 10],[1;0;0]);
plot(t,c(:,1),t,c(:,2),t,c(:,3),'LineWidth',2)

function dcdt = odefun1(t,c)
    dcdt = zeros(3,1);
    dcdt(1) = -c(1)+20*c(2);
    dcdt(2) = c(1)-40*c(2)+c(3);
    dcdt(3) = 20*c(2)-c(3);
end