Overlaying three functions on a single plot

% Peter Daniel Bohlen 
% Mech3080 hw2 
% Part 2E

t = 0: 0.01:6;
x = (6 * exp(-0.5 * t)) * cos((5 * pi * t) + (pi/4));
y = -1.5 * sin(5.5 * pi *t);
z = (6 * exp(-0.5*t))* cos((5 * pi *t) + (pi/4)) - (1.5 * sin(5.5 * pi *t));
plot (t,x)
plot(t,y)
plot(t,z)
grid on 
xlabel 'Time (sec)'
ylabel 'Displacement (in)'
title 'Homework 2 Part 2E - Displacement vs. Time' 

it is returning an error of this :

Error in hw2part2E (line 6)

x = (6 * exp(-0.5 * t)) * cos((5 * pi * t) + (pi/4));

Answer 1

[Voss]

To avoid the error, use element-wise multiplication (.*), because * is for matrix multiplication.

https://www.mathworks.com/help/matlab/matlab_prog/array-vs-matrix-operations.html

To plot multiple functions in a single plot, use hold on.

% Peter Daniel Bohlen 
% Mech3080 hw2 
% Part 2E
t = 0: 0.01:6;
x = (6 * exp(-0.5 * t)) .* cos((5 * pi * t) + (pi/4));
%                       ^^ element-wise

y = -1.5 * sin(5.5 * pi *t);
z = (6 * exp(-0.5*t)).* cos((5 * pi *t) + (pi/4)) - (1.5 * sin(5.5 * pi *t));
%                    ^^ element-wise

figure
hold on

plot (t,x)
plot(t,y)
plot(t,z)
grid on 
xlabel 'Time (sec)'
ylabel 'Displacement (in)'
title 'Homework 2 Part 2E - Displacement vs. Time' 

[Voss]

In this case, since the x, y, and z vectors are all defined in terms of the same vector t, an alternative to using hold on is to plot them all in a single plot call:

% Peter Daniel Bohlen 
% Mech3080 hw2 
% Part 2E
t = 0: 0.01:6;
x = (6 * exp(-0.5 * t)) .* cos((5 * pi * t) + (pi/4));
y = -1.5 * sin(5.5 * pi *t);
z = (6 * exp(-0.5*t)).* cos((5 * pi *t) + (pi/4)) - (1.5 * sin(5.5 * pi *t));
plot(t,[x; y; z].')
grid on 
xlabel 'Time (sec)'
ylabel 'Displacement (in)'
title 'Homework 2 Part 2E - Displacement vs. Time' 

[Peter Bohlen]

Thank you very much!

[Voss]

You're welcome! Any questions, let me know. Otherwise, please "Accept" this answer. Thanks!