Thread: MATLAB Plotting Fourier series coefficients

I'm trying to plot the above fourier series coefficients, what am I doing wrong? here is my matlab code:

Code:

clear
time=-1:0.01:1;
l=0.5;

x=0; %initialize to 0 

for n=1:40
if (n==2*l), x=x-(1/(pi*l)); end;  
if (n==(2*l+1)), x=x+(2/((pi*(2*l+1))))*(1+(2*(-1)^l)/(pi*(2*l+1))); end;
plot(time,real(x))
xlabel('time (sec)')
ylabel('x(t)')
title(['n=', int2str(n), ' Fourier Series Approximation'])
pause(1)
end

Originally Posted by synnexster

I'm trying to plot the above fourier series coefficients, what am I doing wrong? here is my matlab code:

Code:

clear
time=-1:0.01:1;
l=0.5;
 
x=0; %initialize to 0 
 
for n=1:40
  if (n==2*l), x=x-(1/(pi*l)); end;  
  if (n==(2*l+1))
     x=x+(2/((pi*(2*l+1))))*(1+(2*(-1)^l)/(pi*(2*l+1)));
  end;
  plot(time,real(x))
  xlabel('time (sec)')
  ylabel('x(t)')
  title(['n=', int2str(n), ' Fourier Series Approximation'])
  pause(1)
end

1. Don't use l as a variable name, it is too easy to confuse it with 1.

2. l is a constant, so the loop only does anything when n=1, and n=2.

3. It looks as though you intend x to be an array, but its only a scalar.

4. It is not clear what you are trying to do here.

The following creates an array of the coefficients:

Code:

clear
 
b=zeros(1,40); %initialize to a row vector of 40 0's 
 
for n=1:40
  if (mod(n,2)==0)
     L=n/2;
     b(n)= -1/(pi*L); 
  else
     L=(n+1)/2;
     b(n)=2/((pi*(2*L+1))))*(1+(2*(-1)^L)/(pi*(2*L+1));
  end
end

.