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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

KSSV
on 24 Apr 2020

Edited: KSSV
on 24 Apr 2020

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)

Deepak Gupta
on 24 Apr 2020

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)

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