Example 3.13.  Show that  [Graphics:Images/HarmonicFunctionMod._gr_113.gif]  is a harmonic function and find the harmonic conjugate  [Graphics:Images/HarmonicFunctionMod._gr_114.gif].

Explore Solution 3.13.

Enter the function u[x,y], do a step by step construction.

[Graphics:../Images/HarmonicFunctionMod._gr_125.gif]




[Graphics:../Images/HarmonicFunctionMod._gr_126.gif]

[Graphics:../Images/HarmonicFunctionMod._gr_127.gif]

 

 

 

 

[Graphics:../Images/HarmonicFunctionMod._gr_128.gif]


[Graphics:../Images/HarmonicFunctionMod._gr_129.gif]

[Graphics:../Images/HarmonicFunctionMod._gr_130.gif]

 

 

 

[Graphics:../Images/HarmonicFunctionMod._gr_131.gif]


[Graphics:../Images/HarmonicFunctionMod._gr_132.gif]

[Graphics:../Images/HarmonicFunctionMod._gr_133.gif]

 

 

 

[Graphics:../Images/HarmonicFunctionMod._gr_134.gif]


[Graphics:../Images/HarmonicFunctionMod._gr_135.gif]

[Graphics:../Images/HarmonicFunctionMod._gr_136.gif]

 

 

 

We are done!

Aside.  We can also construct v[x,y] by the following alternative method.

Enter the function u[x,y], and determine if it is a harmonic function.  If so, proceed with the construction of the harmonic conjugate v[x,y].

[Graphics:../Images/HarmonicFunctionMod._gr_137.gif]


[Graphics:../Images/HarmonicFunctionMod._gr_138.gif]

 

 

Form the analytic function  f[z] = u[x,y]+ i v[x,y]  and verify that the Cauchy-Riemann equations hold.

[Graphics:../Images/HarmonicFunctionMod._gr_139.gif]



[Graphics:../Images/HarmonicFunctionMod._gr_140.gif]

 

 

Therefore  [Graphics:../Images/HarmonicFunctionMod._gr_141.gif] is the harmonic conjugate of  [Graphics:../Images/HarmonicFunctionMod._gr_142.gif].  

Aside.
  We can use Mathematica to get the standard form of an analytic function.  

[Graphics:../Images/HarmonicFunctionMod._gr_143.gif]



[Graphics:../Images/HarmonicFunctionMod._gr_144.gif]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(c) 2006 John H. Mathews, Russell W. Howell