Signals and Systems - Electrical Engineering

0.5 Soft Introduction to MATLAB 45

0 1 2 3 4 5 6

− 1

−0.5

0

0.5

1

t

cos (t^2 )

(a)

(b)

0 1 2 3 4 5 6

− 10

− 5

0

5

10

t

−2 sin (t^2 ) t

Derivative (black)

Difference (blue)

FIGURE 0.21
Symbolic and numeric computation of the derivative of the chirpy(t)=cos(t^2 ). (a)y(t)and the sampled signal
y(nTs),Ts=0.1sec. (b) Displays the exact derivative (continuous line) and the approximation of the derivative at
samplesnTs. Better approximation to the derivative can be obtained by using a smaller value ofTs.

the functiondiffto approximate the derivative (the denominatordiff(t1)is the same asTs). Plot-
ting the exact derivative (continuous line) with the approximated one (samples) usingstemclarifies
that the numeric computation is an approximation atnTsvalues of time. See Figure 0.21.

The Sinc Function and Integration
The sinc function is very significant in the theory of signals and systems. It is defined as

y(t)=

sinπt

πt

−∞<t<∞

It is symmetric with respect to the origin, and defined from−∞to∞. The value ofy( 0 )can be found
using L’Hopital’s rule. We will see later (Parseval’s result in Chapter 5) that the integral ofˆ y^2 (t)is