Plot Legend Not Correct

So I have a code and want to plot a couple of features. Long story short, my plot legend is a little confused as to its labels. How can I correct this?

 clear;clc;
%inputs
d=5; %feet
h=10; %feet
yi=7; %feet
ysp=5; %feet
dt=30; %seconds
band=1; %feet

 %givens
Vimax=100; %gallons per minute
Vimax=Vimax*0.002228; %ft^3/s
aTank=(pi*d^2)/4; %ft^2
tmax=3000;

 uL=ysp+band/2;
lL=ysp-band/2;

 %valve position
if yi>uL
    vp=0;
elseif yi<lL
    vp=1;
else
    vp=0;
end
t=0;
y=yi;
n=1;
    while t(n)<=tmax
    %net flow rate
    nfl=Vimax*vp-Vout(t); %ft^3/s

    %net volume change for a time step
    vc=nfl*dt; %ft^3

    %determine change in water level
    dy=vc/aTank; %feet
    y(n+1)=y(n)+dy;
    t(n+1)=t(n)+dt;

    %next
    if y(n+1)>uL
        vp=0;
    elseif y(n+1)<lL
        vp=1;
    else
        vp=vp;
        %vp=-(y(n+1)-ysp)/band+0.5; %CHANGE TO PROPORTIONAL
    end
    n=n+1;
    end
     plot(t,y,'r')     
     hold on
     plot(t,ysp,'g+')
     plot(t,uL,'bo')
     plot(t,lL,'y.')
     xlabel('Time in Seconds')
     ylabel('Water Level in Feet')
     legend('Water Level','Setpoint','Upper Level','Lower Level')

Answer 1

[Adam Danz]

The reason your legend has duplicate symbols is because there are multiple elements plotted for each marker. This is one of the reasons why you should used handles when you call legend().

Replace the plotting section after the while loop with this.

h1 = plot(t,y,'r');
hold on
h2 = plot(t,ysp,'g+');
h3 = plot(t,uL,'bo');
h4 = plot(t,lL,'y.');
xlabel('Time in Seconds')
ylabel('Water Level in Feet')
legend([h1,h2(1),h3(1),h4(1)], 'Water Level','Setpoint','Upper Level','Lower Level')

By the way, I couldn't run your code because the value of 'Vout' is unknown.

[Bailey Smith]

I have a function that's called into the code. I totally forgot about that. My bad. And thank you so much for the help!

[Parasram Siewlal]

Thanks, I ran into the same problem and your solution helped.

Answer 2

[Rik]

You can use the output of the plot function to get the handles to the objects. Then you can use the list as an input to legend.

temp=plot(t,y,'r');
plothandles=temp(1);
hold on
temp=plot(t,ysp,'g+');
plothandles(2)=temp(1);
temp=plot(t,uL,'bo');
plothandles(3)=temp(1);
temp=plot(t,lL,'y.');
plothandles(4)=temp(1);
xlabel('Time in Seconds')
ylabel('Water Level in Feet')
legend(plothandles,{'Water Level','Setpoint','Upper Level','Lower Level'})