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Dennis
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Plotting the convolution of two signals

Asked by Dennis
on 23 Oct 2014
Latest activity Commented on by Celeste MacNeil on 14 Oct 2018 at 6:01

I am given two functions x(t) =5[u(t+1)-u(t-1)] and h(t)=u(t-1)-u(t-7). I am asked to convolve these two signals and plot the result in the range -3 to 10. Here is the code that I wrote:

t=-3:0.1:10; t_c=-3:0.05:10; h_t=heaviside(t-1)-heaviside(t-7); x_t1=5.*(heaviside(t+1)-heaviside(t-1)); c_x_h=conv(x_t1,h_t); figure(1) plot(t_c,c_x_h)

However, since this is a simple convolution I verified it by hand and it does not look like the plot i get in MATLAB. The max value should be 10 but in MATLAB i get 100. Also, the duration of the function should be 8 but i get 4 with MATLAB. Please help.

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2 Answers

Answer by Rick Rosson
on 23 Oct 2014
 Accepted Answer

Please try:

   t_c = -6:0.1:20;

and:

   dt = t(2) - t(1);
   c_x_h = dt*conv(x_t1,h_t); 

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What is dt = t(2)-t(1)? What does it mean?

What do you mean dt = t(2)-t(1)?

I assume you just mean the step?

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Answer by IKRAM jebali on 31 Mar 2017

Hello! Thank you. I'had the same problem. Me too amnclear as to why the dt is needed though and why t_c needed to be extended to -6 to 20. I use it but i don't know why? There is any answer please. Thank you.

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Because the length of the convolution of two matrices of ,length m and n will be m+n-1. inorder to get the same vector size, you need to do this.

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