Plotting damped sine travelling wave equation in Matlab

Question

Jesse 2015-2-20

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回答： Jesse 2020-4-24

Greetings all,

Please correct me if I am wrong on any of this, but I am trying to plot a damped/attenuating sine wave of the form y(x,t)=Ae^-alpha(x) * sin(wt-Bx + phi).

Granted the sin is not in the exponential, I've been trying to code this up knowing that travelling waves have spatial as well as temporal dimensions.

The code I have after user input is:

x=0:.001:1;
Beta = 2*pi/lambda; %(lambda is user input)
y1=zeros(100,100);
for t=0:.001:1
y1(t,:)=A*sin(Beta*x-w*t + phi).exp(-alpha*x)
end

%A, alpha, w, and phi are user input as well

So I'm getting a "Subscript indices must be either real positive integers or logicals." Where am I going wrong?

Also, I am trying to plot this damped wave - do I need to use plot3? If so, why?

Thanks!

-J

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Prasad Reddy 2020-4-24

y1(t,:)=A*sinBeta.*x-w*t+phi).*exp(-alpha.*x)

please check the above equation. it may work.

you need not to use plot3 command.

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Answer 1

KSSV 2020-4-24

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编辑：KSSV 2020-4-24

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You index t, is taking zero for the first time. Indices cannot be negative and zero in MATLAB. You need not to use loop, you can follow as below.

clc; clear al ;
A = rand ; 
lambda = rand ; 
w = rand ; 
phi = rand ; 
alpha = rand ; 
x=0:.001:1;
Beta = 2*pi/lambda; %(lambda is user input)
t=0:.001:1 ; 
[X,T] = meshgrid(x,t) ; 
Y1 = A*sin(Beta*X-w*T + phi).*exp(-alpha*X) ; 
surf(X,T,Y1)

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Answer 2

Deepak Gupta 2020-4-24

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在 MATLAB Online 中打开

Your y1 seems to be function of two variables x and t so yes, you will need to use plot3 at it will plot y1 against two variables.

You can try below code to find value of y1:

x=0:.001:1;
t =(0:.001:1)';
Beta = 2*pi/lambda; %(lambda is user input)
y1=zeros(1001,1001); % y1 should have same dimention as x*t matrix.
y1=A*sin(Beta*x-w*t + phi).*exp(-alpha*x)
plot3(t, x, y1)