| Line 22: | Line 22: | ||
we determine: | we determine: | ||
<math> x[n] = cos(\pi*n) = \frac{e^{j*\pi*n} + e^{-j*\pi*n}}{2} </math> | <math> x[n] = cos(\pi*n) = \frac{e^{j*\pi*n} + e^{-j*\pi*n}}{2} </math> | ||
| + | |||
yields to <math> x[t*n] = \frac{te^{j*\pi*n} + t*e^{-j*\pi*n}}{2} </math> | yields to <math> x[t*n] = \frac{te^{j*\pi*n} + t*e^{-j*\pi*n}}{2} </math> | ||
| + | |||
| + | <math> == cos(\pi*n) -> -1 </math> on every even integer interval. | ||
Revision as of 14:35, 18 September 2008
The Basics of Linearity
A system is linear if its inputs are sequentially equal to the outputs for a certain function:
$ x(t) = a*x1(t) + b*x2(t) = a*y1(t) + b*y2(t) $
Take for a simple example:
Ex) What is the output of:
$ x[n] = e^{j*\pi*n} -> n*e^{-j*\pi*n} $
$ x[n] \to Sys 1 \to n*x[-n] $
from:
$ e^{j*n*y} = cos(n*y) + j*sin(n*y) $
we determine: $ x[n] = cos(\pi*n) = \frac{e^{j*\pi*n} + e^{-j*\pi*n}}{2} $
yields to $ x[t*n] = \frac{te^{j*\pi*n} + t*e^{-j*\pi*n}}{2} $
$ == cos(\pi*n) -> -1 $ on every even integer interval.
