Solving PDE w/ complex Neumann boundary condition

Hi,

I am working on combustion instabilities and therefore looking into eigenmodes. To solve for the pressure distribution u, I have to define my boundary conditions. As I understood from the Mathworks website, the Neumann BC is written in a general form as grad(u) + q * u = g. I am able to solve for real values of q (and I'm setting g=0), this being one of my BC:

    neumann =   [1 0 6 6 '0.1000' '0.0000']';

Can anybody tell me if there is a possibility to extent q values to imaginary values and thus q = q_r + iq_i?

Regards,

Simon R2011a

Answer 1

[Bill Greene]

Hi,

The expression within the single quotes has to be a valid MATLAB arithmetic expression. To define a complex number in MATLAB do either:

a + i*b

or

a + sqrt(-1)*b

The second form can be useful when the variable i has been redefined for some other purpose such as a loop index. So, in some ways, it is safer.

Bill

Answer 2

[Bill Greene]

Hi,

Yes, PDE Toolbox allows the BC (or PDE) coefficients to be imaginary. Are you running into a particular problem?

Bill

Answer 3

[Simon]

Hi Bill,

Thanks for your answer. What is the syntaxis of an complex BC? Matlab does not allow it to be defined this way:

neumann =  [1 0 6 6 'a + ib' '0.0000']'

Do you know how it should be defined?

Thanks!

Answer 4

[Simon]

hi Bill,

That just works! Great.

The eigenmodes u however, returned by pde function, are complex. Do you have any experience with complex eigenmode interpretation?

Thanks a lot.

Simon