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$y(n) = x(-n)$ , causal or not , memory or memory-less ?

it's a question in digital signal processing course .

My guess it's memory less , causal because $x(-n)$ is only the inverse of the function ?

Memoryless System A system is memoryless if the output y[n] at every value of n depends only on the input x[n] at the same value of n

Causality A system is causal it’s output is a function of only the current and previous samples

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It helps (you and the others) that the problem statement has a subject and a predicate. Eg: Is the filter/system defined by the relation $y[n]=x[-n]$ causal or not... ? ($x[n]$ is the input and $y[n]$ the output? Do you know the definition of a memory-less filter? What is the output at time, say $n=5$? –  leonbloy Jun 1 '12 at 23:39
I got it in the sheet like , tell whether the system is memory or memory less, causal or non –  xsari3x Jun 1 '12 at 23:56
well, a system is memoriles if output y[n] for every value of n (say, for n=5, y[5]) depends only of the input at the same instant (x[5]) But y[5] does depend rather on x[-5], so... –  leonbloy Jun 2 '12 at 1:02
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1 Answer

up vote 1 down vote accepted
  • It is not causal. Consider $n=-1$. The output $y(-1)$ depends on the input at $n=1$, which is only available in future.
  • It is not memoryless. Consider any $n > 0$. The output $y$ depends on the input at $-n$ which was applied in the past. Thus the system has memory.
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