Legend is applied to incorrect figure

So, I run several simulations in SimuLink, store lots of variables and them plot them variously on different figures. I would like some of the same plots to appear on different figures, so I've been doing something like:

%%plot results

% plot ideal sim
figure(1), hold on
h_step = plot(time, dtheta_ideal/(2*pi)*60, 'b') % dtheta in rpm
xlabel('Time (s)'); ylabel('Speed (RPM)');
title('Ideal second order model of DC motor')
legend ('open loop step response')

% plot idealPID0 sim
figure(2), hold on
hstep = plot(time, dtheta_ideal, 'b')
hKp = plot(time, dtheta, 'g');
hv_demand_Kp = plot(time, control, 'm')
hKp_ref = plot([0 time(end)], [ref ref], 'r')
plot(time, refsig, 'r')

xlabel('Time (s)'); ylabel('response');
title('Speed control of ideal 2nd order DC motor with Kp = 0.9 and Ki = 0')

legend([h_step, hKp_ref, hKp, hv_demand_Kp],...
  {'Open loop step response (rad/s)',...
  'reference signal (rad/s)',...
  'proportional control response',...
  'proportional control demand (V)'})

% repeat ad nauseam %

I would like and expect this to generate two plots, titled and with appropriate legends. What ACTUALLY happens is the legend designated for figure 2 shows up on figure 1, with no warnings written to the output (i.e. 'Open loop step response', 'reference signal' etc. show up on figure 1). The original legend for figure 1 is gone, and all the labels appear as I would 'expect' them to. Is there a way to explicitly specify which figure to put a plot on, or am I doing something deserving of an RTFM?

Answer 1

[Image Analyst]

Looks like it should work, but if it doesn't, you can explicitly pass in the axes to plot() and legend():

hFig2 = figure(2);
legend(hFig2, [h_step, hKp_ref, hKp, hv_demand_Kp],...
  {'Open loop step response (rad/s)',...
  'reference signal (rad/s)',...
  'proportional control response',...
  'proportional control demand (V)'})

[agentroadkill]

This yields an error: Handle inputs of type Figure cannot be used with this function

[Walter Roberson]

You cannot pass figures to legend(). legend() will examine the ancestor() 'figure' of the handles that you pass in to determine which figure to draw the legend in.

Answer 2

[Star Strider]

I cannot run your code, but the reason the second legend call shows up in your first plot (with the ‘h_step’ handle) is that you told it to:

legend([h_step, hKp_ref, hKp, hv_demand_Kp],...

       ^^^^^^

[agentroadkill]

Ah. I fudged my own syntax. Thank you

[Star Strider]

My pleasure.

It’s the benefit of my seeing it for the first time.