Probability and complex function: Unit III: Analytic functions

Construction of analytic function

There are three methods to find f (z).

CONSTRUCTION OF ANALYTIC FUNCTION

There are three methods to find f (z).

Method 1. Exact differential method.

(i) Suppose the harmonic function u (x, y) is given.

Now, dv = vx dx + vy dy is an exact differential

where vx and vy are known from u by using C-R equations.


(ii) Suppose the harmonic function v (x, y) is given

Now, du = ux dx+uy dy is an exact differential

where ux and uy are known from v by using C-R equations


Method 2. Substitution method

f(z) = 2u [ ½ ( z + a), -i/2 (z - a) ] – [ u(a,0), -iv(a,0)]

Here, u (a, 0) — iv (a, 0) is a constant

Thus f(z) = 2u [1/2 (z + a), -i/2(z - a)] + C

By taking a = 0, that is, if f (z) is analytic at z = 0 + i0,

we have the simpler formula for f (z)

f(z) = 2 [u(z/2 , -iz/2)] + C

Method 3 [Milne-Thomson method]

(i) To find f (z) when u is given

Let f (z) = u + iv

f' (z) = ux + ivx

= ux - iuy [by C.R., condition]


where C is a complex constant.

(ii) To find f (z) when v is given

Let f (z) = = u + iv

f' (z) = ux + ivx

= vy + i vx [by C.R., condition]


where C is a complex constant.

Probability and complex function: Unit III: Analytic functions : Tag: : - Construction of analytic function