Translations:Inverse filters/21/en

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Let us now illustrate this point, although for the moment we shall speak metaphorically. We live in a world in which we know only a one-way flow of time. Everything we do is subject to this unidirectional flow. Now let us look at the two-faced Roman god Janus (after whom the month of January is named). Janus can see both forward and backward in time. We can see only backward in time - that is, we can see only the history of a time series up to the present time n, and we cannot see the future development of the time series, no matter how hard we try. However, Janus can see that future just as well as he can see the past. To him, time is not a unidirectional flow. He has a vantage point denied to us. How can we reach that vantage point? We can reach it only by waiting - that is, by delaying - until a finite amount of time has passed, during which period some or most of the information required for stability has become past history. Thus, to reach for stability in our feedback filter, we must delay our output. The greater the delay is, the greater are our chances.