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Problems<br />

6S<br />

magnitude. The program provides the residues corresponding to the order in<br />

which the roots were furnished and in descending root multiplicity. The<br />

residue output order can be understood best by running the example appearing<br />

in Figure 3.9 and comparing the results. A Laplace transformation to the<br />

time domain was illustrated as one <strong>of</strong> many important applications <strong>of</strong> the<br />

partial fraction expansion program.<br />

Problems<br />

3.1. Differentiate<br />

using the calculus formula<br />

Differentiate<br />

f(z)=(z-I)(z-2)2<br />

d(uvw)=vwdu+uwdv+ uvdw.<br />

fez) =z'-5z 2 +8z-4<br />

and evaluate f'(2). Note why the derivative <strong>of</strong> polynomials with multiple<br />

roots is zero at the root.<br />

3.2. Given the polynomial<br />

fez) =z' = (x + jY)' = (x' - 3xy2) + j(3x 2 y - y') = u + jv.<br />

(a)<br />

(b)<br />

(c)<br />

Find derivative df/ dz by differentiation.<br />

Find derivative df/dz using the Cauchy-Riemann identity.<br />

Show, using fez), that<br />

au = av and av = _ au<br />

ax ay ax ay'<br />

3.3. Given the complex polynomial<br />

fez) = 5+3z+2z 2 +4z'-2z 4 =u+jv<br />

for z=x+jy, use the Mitrovic method to find numerically the values <strong>of</strong><br />

u, v, and the following derivatives when z = I + j3:<br />

au av au d av<br />

ax' ax' ay' an ay .<br />

3.4. A root finder has located root Z. = -!- jff/2 <strong>of</strong> the polynomial equation<br />

f(z) = 2z'+9z 4 + 13z'+z2-13z+4=0.

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