Plot Two Signals on the Same Axes in MATLAB

Method 1: Using hold on (Standard Approach)

Use hold on to retain the current plot when adding subsequent signals. This method works well when both signals share similar units and scales.

% Time vector and signals
t = linspace(0, 1, 1000);
signal1 = sin(2 * pi * 5 * t);          % 5 Hz sine wave
signal2 = 0.5 * cos(2 * pi * 10 * t);   % 10 Hz cosine wave

figure('Color', 'w');
% Plot first signal
plot(t, signal1, 'b-', 'LineWidth', 1.5);
hold on;
% Plot second signal
plot(t, signal2, 'r--', 'LineWidth', 1.5);
hold off;
% Add formatting
grid on;
xlabel('Time (s)');
ylabel('Amplitude (V)');
title('Two Signals on the Same Axes');
legend('Signal 1 (5 Hz Sine)', 'Signal 2 (10 Hz Cosine)', 'Location', 'northeast');

Method 2: Multiple Inputs in a Single plot() Command

Pass coordinate pairs directly into one plot() call.

t = linspace(0, 2*pi, 200);
y1 = sin(t);
y2 = cos(t);

figure('Color', 'w');
plot(t, y1, 'b-', t, y2, 'm-.', 'LineWidth', 1.8);
grid on;
xlabel('Angle (rad)');
ylabel('Value');
legend('sin(t)', 'cos(t)');

Method 3: Two Signals with Different Scales (yyaxis)

When signals have different units or magnitudes (for example, voltage and current), use yyaxis to create independent left and right y-axes on the same figure.

t = linspace(0, 0.05, 500);
voltage = 230 * sin(2 * pi * 50 * t);   % Large magnitude (Volts)
current = 2.5 * sin(2 * pi * 50 * t - pi/6); % Small magnitude (Amperes)

figure('Color', 'w');
% Left Y-axis for Voltage
yyaxis left
plot(t, voltage, 'b-', 'LineWidth', 1.5);
ylabel('Voltage (V)');
ylim([-300 300]);
% Right Y-axis for Current
yyaxis right
plot(t, current, 'r--', 'LineWidth', 1.5);
ylabel('Current (A)');
ylim([-4 4]);
% Shared formatting
xlabel('Time (s)');
title('Voltage and Current on Dual Y-Axes');
grid on;
legend('Voltage', 'Current', 'Location', 'northeast');

Method 4: Matrix Input (Column-Wise Plotting)

If signals share the exact same time vector and dimensions, combine them into matrix columns.

t = (0:0.001:1)';
Y = [sin(2*pi*3*t), cos(2*pi*3*t)]; % 1001-by-2 matrix

figure('Color', 'w');
plot(t, Y, 'LineWidth', 1.5);
grid on;
xlabel('Time (s)');
ylabel('Amplitude');
legend('Channel 1', 'Channel 2');