I have the following two graphs but I don't know how to recognize from the graph if they are IIR or FIR! Can you please guide me through? enter image description here

P.S.: Does MATLAB have a function to detect if an impulse response graph corresponds to IIR or FIR?

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    $\begingroup$ Think 'infinite' (top graph) vs. 'finite' (bottom graph) impulse response. One further way to tell is to transform the impulse response. That will tell you (in the frequency domain) what the filter will do to an input signal. If the phase of the transformed impulse response is linear - it's probably a FIR. If not - it's probably an IIR. But there are no guarantees - there are many different ways of designing filters with different characteristics. $\endgroup$ – Kevin McGee Feb 22 '14 at 2:21

If a filter is FIR then the impulse response is finite and goes to zero and stays there. This is like the second filter in your post. If it is IIR the impule response extends towards infinity like the first image in your post


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