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XE31CZS exercise - Discrete-time systems, difference equation, transfer function.

**Tasks to do: **

- For discrete-time systems described by following difference
equations draw block scheme, evaluate transfer function and impulse
response a estimate frequency response.
- y[n] = x[n] + x[n-1] + x[n-2] + x[n-3] ;
- y[n] = x[n] - x[n-6] ;
- y[n] = x[n] - x[n-1] ; ( y[n] = x[n] - 0.95 x[n-1] ; )
- y[n] = x[n] - 0.9 y[n-1] ;
- y[n] = x[n] - 0.81 y[n-2] ;

- For above described system observe in MATLAB:
- zeros and poles of transfer function (fnc
*zplane*, *roots*).
- frequency response (fnc
*freqz*).