0 个投票

I'm new to Matlab and I'm trying to plot the velocity related to the function for a damped harmonic oscillator. I have been able to plot the function itself, but when I try to plot the velocity of said function, I receive this error:
Error using plot
Vectors must be the same length.
Error in damped_oscillator (line 102)
plot(t,v);
I'm not sure how to solve this problem. I've linked the original code. Any help is much appreciated!

请先登录，再回答此问题。

 采纳的回答

KALYAN ACHARJYA
KALYAN ACHARJYA 2019-9-22
编辑：KALYAN ACHARJYA 2019-9-22

0 个投票

You can make the privious three plot in single description using for loop, define "a" in array. #Recomended. The error arises because of non equal length of t and v, as v result from diff. Hence I have ignored the last element of t to make them both equal. You can opt out the first one also, as per your requirements.
m=20; %Mass
k=30; %Spring constant
c=0.9; %Damping constant
A=1;
a=0;
g=c/(2*m); %Damping coefficient
wn=sqrt(k/m); %Natural frequency
wd=sqrt(((wn)^2)-(g)^2); %Damped natural frequency
t=linspace(0,40,1000); %Time value
x=A*exp(-g*t).*cos(wd*t-a); %x(t)
subplot(4,3,1),plot(t,x)
title('Question 1')
xlabel('Time')
ylabel('Displacement (m)');
grid on;
c=0.9; %Damping constant
A=1;
a=0;
g= c/(2*m); %Damping coefficient
wn=sqrt(k/m); %Natural frequency
wd=sqrt(((wn)^2)-(g)^2); %Damped natural frequency
t=linspace(0,20,1000); %Time value
x=A*exp(-g*t).*cos(wd*t-a); %x(t)
subplot(4,2,1),plot(t,x)
title('Question 2')
xlabel('Time (s)')
ylabel('Displacement (m)')
grid on;
c=0; %Damping constant
A=1;
a=0;
g= c/(2*m); %Damping coefficient
wn=sqrt(k/m); %Natural frequency
wd=sqrt(((wn)^2)-(g)^2); %Damped natural frequency
t=linspace(0,40,1000); %Time value
x=A*exp(-g*t).*cos(wd*t-a); %x(t)
subplot(4,2,2),plot(t,x)
title('Question 3')
xlabel('Time (s)')
ylabel('Displacement (m)')
grid on;
c=1; %Damping constant
A=1;
a=0;
g= c/(2*m); %Damping coefficient
wn=sqrt(k/m); %Natural frequency
wd=sqrt(((wn)^2)-(g)^2); %Damped natural frequency
t=linspace(0,40,1000); %Time value
x=A*exp(-g*t).*cos(wd*t-a); %x(t)
subplot(4,2,3),plot(t,x)
c=5; %Damping constant
A=1;
a=0;
g= c/(2*m); %Damping coefficient
wn=sqrt(k/m); %Natural frequency
wd=sqrt(((wn)^2)-(g)^2); %Damped natural frequency
t=linspace(0,40,1000); %Time value
x=A*exp(-g*t).*cos(wd*t-a); %x(t)
subplot(4,2,4),plot(t,x)
c=15; %Damping constant
A=1;
a=0;
g= c/(2*m); %Damping coefficient
wn=sqrt(k/m); %Natural frequency
wd=sqrt(((wn)^2)-(g)^2); %Damped natural frequency
t=linspace(0,40,1000); %Time value
x=A*exp(-g*t).*cos(wd*t-a); %x(t)
subplot(4,2,5),plot(t,x)
c=50; %Damping constant
A=1;
a=0;
g= c/(2*m); %Damping coefficient
wn=sqrt(k/m); %Natural frequency
wd=sqrt(((wn)^2)-(g)^2); %Damped natural frequency
t=linspace(0,40,1000); %Time value
x=A*exp(-g*t).*cos(wd*t-a); %x(t)
subplot(4,2,6),plot(t,x)
legend('0','1','5','15','50')
t=linspace(0,40,1000); %Time value
x=A*exp(-g.*t).*cos(wd.*t-a); %x(t)
v=diff(x)./diff(t); %Velocity
subplot(4,2,7),plot(t(1:end-1),v);

更多回答（1 个）

MS
MS 2019-9-22
编辑：MS 2019-9-22

0 个投票

The two vectors have different sizes. Since you are using the diff function. From documentation:
Y = diff(X) calculates differences between adjacent elements of X along the first array dimension whose size does not equal 1:
  • If X is a vector of length m, then Y = diff(X) returns a vector of length m-1.
Hence, the t vector has a size of 1 x1000 and the v vector has a size of 1x 999.
if you want, you can update t by removing the first element where the speed is not calculated:
t = t(2:1000)
plot(t,v);

类别

在 帮助中心 和 File Exchange 中查找有关 Numerical Integration and Differential Equations 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by