Editing Linear system (section)

==Discrete-time systems==
The output of any discrete time linear system is related to the input by the time-varying convolution sum:
<math display="block"> y[n] = \sum_{m =-\infty}^{n} { h[n,m] x[m] }  = \sum_{m =-\infty}^{\infty} { h[n,m] x[m] }</math>
or equivalently for a time-invariant system on redefining {{math|''h''}},
<math display="block"> y[n] = \sum_{k =0}^{\infty} { h[k] x[n-k] } = \sum_{k =-\infty}^{\infty} { h[k] x[n-k] }</math>
where <math display="block"> k = n-m </math> represents the lag time between the stimulus at time ''m'' and the response at time ''n''.