I am trying to plot different curves in gui, but i dont know how to add legend to it.

My plots depend on a single variable 's' which i take from the user. I get the plot but am unable to get all the legends for different plots that the user plot for different 's' values. This is the plotting part of the code. where 'i' is a global parameter which increments with each new value of 's'.

   p(i)= plot(x,y,'linewidth',2,'Color',clr(i));
    hold on
    grid on
        title('Rotor Voltage Limit for Various Slip values')
xlabel('P');
ylabel('Q');
 Legend{i}=strcat('S=', num2str(s));

 for l=1:i
 legend([p(1:l)],Legend{1:l})
 end

[Rik]

My first observation is that you don't need the for-loop. The legend function also works if you just enter an array of handles and a cell array. My second observation is that the curly brackets look wrong, as you will not be supplying a cell array as second parameter. I bet you got an error for l==2 (as for l==1 you were just adding a single element legend).

[Ankit Singh]

YES! I did get an error for l==2. So what am I supposed to do.

Answer 1

[Rik]

Try if this works: replace this

for l=1:i
legend([p(1:l)],Legend{1:l})
end

with this

 legend(p(1:i),Legend(1:i))

[Ankit Singh]

Doesn't work, "Invalid argument" error again.

[Ankit Singh]

Should I keep the curly brackets as it is, in Legend {}. Here "i" is a global parameter which increments every time a new s value is entered.

[Rik]

Could you copy the entire error stack?

I also advise you to use the step-by-step functionality of the debugger. It is ideal for finding out things like clearing/overwriting variables or small but significant errors in calculation.

[Ankit Singh]

Is this the error stack?

 Error using legend (line 120)
Invalid argument. Type 'help legend' for more information.
Error in RotorVoltageGUI>pushbutton1_Callback (line 144)
legend(p(1:i),Legend(1:i))
Error in gui_mainfcn (line 95)
        feval(varargin{:});
Error in RotorVoltageGUI (line 42)
    gui_mainfcn(gui_State, varargin{:});
Error in @(hObject,eventdata)RotorVoltageGUI('pushbutton1_Callback',hObject,eventdata,guidata(hObject))
Error while evaluating UIControl Callback

[Ankit Singh]

I'm sorry to bother you so much sir, but here is the complete .m file of my gui. If you could please help me correct this simple error.

[Rik]

Ah, I found the problem. Your variable Legend does not grow, but only has a single element. I would advise you to add both i and Legend to the handles structure, as that is much easier to debug than a global.

And if you were posting too much for me, you would simply not get a fast answer ;)

[Ankit Singh]

How do I add them to handles structure?

[Rik]

You do have to initialize the value, so some line like if ~isfield(handles,'i'),handles.i=0;end So that might be one problem.

The other thing I notice is you are still calling Legend in the legend command, instead of handles.Legend.

If this gets too difficult, I advise you to change the name of i to a more unique name (something like Rotor_Voltage_Plot_counter), so you are less likely to overwrite it, and then make it global. (and do the same for Legend)

And remember, if you get an error, ALWAYS at least mention the error itself, and preferably the entire error stack. Otherwise we need to guess where the problem occurs. A free tip: use the 'stop on error': it will show you where your code breaks and the values of your variables.

[Ankit Singh]

I tried changing the names to "counter" and "legend_name" still getting the following error.

if true
Error using legend (line 120)
Invalid argument. Type 'help legend' for more information.
Error in RotorVoltageGUI>pushbutton1_Callback (line 132)
legend(p(1:counter),legend_name(1:counter))
Error in gui_mainfcn (line 95)
      feval(varargin{:});
Error in RotorVoltageGUI (line 42)
  gui_mainfcn(gui_State, varargin{:});
Error in @(hObject,eventdata)RotorVoltageGUI('pushbutton1_Callback',hObject,eventdata,guidata(hObject))
end

[Ankit Singh]

And stop on error shows there is error in legend command

[Rik]

And you set them both as a global?

[Ankit Singh]

Yes.

[Rik]

The handle array p also grows every iteration, so you'll have to set that one as a global as well.

[Ankit Singh]

Ok, I did that, but p is not being used in any other function. Still i'm getting this error.

Error using legend (line 120)
Handle inputs of type double cannot be used with this function.
Error in RotorVoltageGUI>pushbutton1_Callback (line 132)
legend(p(1:counter),legend_name(1:counter))

[Ankit Singh]

Sir, I don't know what happend, but I accidently clicked on the pushbutton plot all, without entering the Vs and S values, and then after entering the Vs and S values, when I press plot all, it works, the legend comes and I dont get any error. Can you tell me how is this happening?

[Ankit Singh]

This is the .m file now, it works perfectly fine if i just press the pushbutton first without entering any values, and then do it after entering the values.

[Ankit Singh]

Sir, I got it! Omg, I was increasing the counter when a new s value was being entered by the user, so the counter was starting from 1+1, 2, instead of 1, and thus all the errors. I feel silly now, to have wasted so much of both of our time. Thank you so much for your help sir. :)

[Rik]

You're welcome. It is often these little typos that make for the most inexplicable problems.