I'm adding legend in the graph for the 4 plot in the same graph, please help me in this.

ti = 0;
tf = 1E-3;
tspan=[ti tf];
y0 = [(10E-6).*rand(10,1);((-3.14).*rand(4,1) + (3.14).*rand(4,1))]; % intial conditions
o = sort(10e2*rand(1,4),'ascend'); %detuning frequency
t =1E-3;
[T,Y]= ode45(@(t,y) rate_eq(t,y,o),tspan,y0);

figure(1)
plot(T./t,(Y(:,11)),'linewidth',0.8);
hold on 
for m = 12:14
    plot(T./tf,(Y(:,m)),'linewidth',0.8);
end 
hold off
grid on
xlabel("time")
ylabel("phase difference")

legend(Y(:,11),Y(:,12),Y(:,13),Y(:,14),"Location","northeast");

Error using legend
Invalid argument. Type 'help legend' for more information.

set(gca,'fontname','times New Roman','fontsize',18,'linewidth',1.8);

function dy = rate_eq(t,y,o)

dy = zeros(14,1);

P = 1.25;
a = 0.1;
tc = 230E-6;
tp = 5.4E-9;

k = 6E-3;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
dy(1) = (P - y(1).*((abs(y(6)))^2 +1))./tc;

dy(2) = (P - y(2).*((abs(y(7)))^2 +1))./tc;

dy(3) = (P - y(3).*((abs(y(8)))^2 +1))./tc;

dy(4) = (P - y(4).*((abs(y(9)))^2 +1))./tc;

dy(5) = (P - y(5).*((abs(y(10)))^2 +1))./tc;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

dy(6)= (y(1)-a).*((y(6))./tp) + (k./tp).*(y(7)).*cos(y(11));

dy(7)= (y(2)-a).*((y(7))./tp) + (k./tp).*(y(8)).*cos(y(12)) + (k./tp).*(y(6))*cos(y(11));

dy(8)= (y(3)-a).*((y(8))./tp) + (k./tp).*(y(9)).*cos(y(13)) + (k./tp).*(y(7))*cos(y(12));

dy(9)= (y(4)-a).*((y(9))./tp) + (k./tp).*(y(10)).*cos(y(14)) + (k./tp).*(y(8))*cos(y(13));

dy(10)= (y(5)-a).*((y(10))./tp) + (k./tp).*(y(9)).*cos(y(14));

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
dy(11) = o(1,1) - (k./tp).*(y(6)/y(7)).*(sin(y(11))) - (k./tp).*(y(7)/y(6)).*(sin(y(11))) + (k./tp).*(y(8)./y(7))*sin(y(12));

dy(12) = o(1,2) - (k./tp).*(y(7)/y(8)).*(sin(y(12))) - (k./tp).*(y(8)/y(7)).*(sin(y(12))) + (k./tp).*(y(9)./y(8))*sin(y(13)) + (k./tp).*(y(6)/y(7)).*sin(y(11));

dy(13) = o(1,3) - (k./tp).*(y(8)/y(9)).*(sin(y(13))) - (k./tp).*(y(9)/y(8)).*(sin(y(13))) + (k./tp).*(y(10)./y(9))*sin(y(14)) + (k./tp).*(y(7)/y(8)).*sin(y(12));

dy(14) = o(1,4) - (k./tp).*(y(9)/y(10)).*(sin(y(14))) - (k./tp).*(y(10)/y(9)).*(sin(y(14))) + (k./tp).*(y(8)/y(9)).*sin(y(13));

end

Answer 1

[dpb]

Use something like

legend('Y(11)','Y(12)','Y(13)','Y(14)',"Location","northeast");

instead.

The legend entries are strings describing the data, not references to the data itself.