MATLAB CONTROL SYSTEM TOOLBOX 9 Guida Utente Scaricare il pdf (Pagina 619)

100

101

11-229

engineers use the variable a nd order the numerator and denominator terms

in descending powers of , for example,

The polynomials and are then specified by the row vectors

[1 0 0] and [1 2 3], respectively. By contrast, DSP engineers prefer to write

this trans fer function as

and specify its numerator as

1 (instead of [1 0 0]) and its denominator as

[1 2 3].

tf switches convention based on your choice of variable (value of the

'Variable' property).

For example,

g = tf([1 1],[1 2 3],0.1)

specifies the discrete transfer function

because is the default variable. In contrast,

h = tf([1 1],[1 2 3],0.1,'variable','z^–1')

Variable Convention

'z'

(default) Use the row vector [ak ... a1 a0] to specify the

polynomial (coefficients ordered in

descending powers of ).

'z^–1', 'q' Use the row vector [b0 b1 ... bk] to specify t he

polynomial (coefficients in

ascending powers of or ).

hz()

2z 3++

----------------------------=

2 z 3++

1–

()

12z

1–

2–

----------------------------------------=

... a

++ +

–

... b

–

+++

–

gz()

z 1

2z 3++

----------------------------=

1 2 ... 614 615 616 617 618 619 620 621 622 623 624 ... 648 649

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MATLAB CONTROL SYSTEM TOOLBOX 9 Guida Utente Pagina 619

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