Can someone please help me correct the error in my code? I'm trying to construct a superposition of two waves of equal amplitude and very similar frequency to create an envelope wave. Thanks

close all
clear all
clc
x=1:0.1:300;
%
a=1;%m
h=10;%m
k1=2*pi/(pi/2);%1/m  where k=2pi/wavelength
k2=2*pi/(pi/1.95);
g=9.81;%m/s^2
w1=sqrt(g*k1*tanh(k1*h)); %rad/s
w2=sqrt(g*k2*tanh(k2*h));
e= -pi + (2*pi).*rand(1,1);% phase is a random number between -pi and pi
T=100;%s
n=zeros(length(x),T);
t=1:0.1:T;
for m=1:length(t)
  n(:,m) = 2*a*cos(((w2-w1)*t(m)*0.5) - ((k2-k1)*x*0.5))) * cos(((w2-w1)*t(m)*0.5) - ((k2-k1)*x*0.5)));
plot(n(:,m),'b-','LineWidth',2);
axis([pi 100*pi -10 10])
title(['Propagating Plane Wave at time, t=' num2str(t(m)) ' s.'])
xlabel('Horizontal Excursion, m')
ylabel('Surface Elevation, m')
drawnow
pause(0.5)
end

Answer 1

[Alberto]

Check the parenthesis in the line:

n(:,m) = 2*a*cos( ( (w2-w1)*t(m)*0.5) - ((k2-k1)*x*0.5))) *... cos( ( (w2-w1)*t(m)*0.5) - ((k2-k1)*x*0.5)));

your problem is there, it depends in

 close all
clear all
clc
x=1:0.1:300;
%
a=1;%m
h=10;%m
k1=2*pi/(pi/2);%1/m  where k=2pi/wavelength
k2=2*pi/(pi/1.95);
g=9.81;%m/s^2
w1=sqrt(g*k1*tanh(k1*h)); %rad/s
w2=sqrt(g*k2*tanh(k2*h));
e= -pi + (2*pi).*rand(1,1);% phase is a random number between -pi and pi
T=100;%s
n=zeros(length(x),T);
t=1:0.1:T;
for m=1:length(t)
 n(:,m) = 2*a*cos( ( (w2-w1)*t(m)*0.5) - ((k2-k1)*x*0.5)).*...
             cos( ( (w2-w1)*t(m)*0.5) - ((k2-k1)*x*0.5));
plot(n(:,m),'b-','LineWidth',2);
axis([pi 100*pi -10 10])
title(['Propagating Plane Wave at time, t=' num2str(t(m)) ' s.'])
xlabel('Horizontal Excursion, m')
ylabel('Surface Elevation, m')
drawnow
pause(0.5) % this is causin error too, you can delete it
end

[trinikotch]

Thanks its working now but I realize Its not the graph I was trying to plot

[Alberto]

The problem was that parenthesis didn't matched: too much parenthesis. Try to rewrite carefully.