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FINITE DIFFERENCE S INTRODUCTION Suppose x(0), x(1),...x(n) are sample input signals and y(0), y(1), ....y(n) output signals as given in Fig. Then we ca n form a table of values x x o  x 1  x 2  x 3  . . . x n-1  x n  y y o  y 1  y 2  y 3  . . . x n-1  y n  If we subtract from each value of y (except y 0 ) the proceeding value of y we get y 1  - y 0 , y 2  - y 1 , .....y n  - y n-1  . These are called as first order forward differences of y and are denoted by y. i. e y 0  = y 1  - y 0 , y 1  = y 2  - y 1 , .... y n-1  = y n  - y n-1 . These are called first differences. From these we can form second order differences 2 y 0  = y 1  - y 0 , 2 y 1  = y 2  - y 1 , ... 2 y n-1  = y 2  - y 1 . If x 0 , x 1 , x 2 , ,, x n  are equally spaced t hen the input sig nals can be written as x 0 + h, x 0 + 2h, ..... x n + h , so tha x 1  - x 0  = h = x 2  - x 1 etc. We now define f(x)= f(x + h) - f(x). Backward Differences: The differences of the form y 1  = y 1  - y 0 , y 2  = y 2  - y 1 , .... y n  = y n  - y n-1 .

Lecture Notes Finite Differences

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