Solving PDE w/ complex Neumann boundary condition

2013 8 16
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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

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Bill Greene
Bill Greene 2013-8-17

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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

更多回答（3 个）

Bill Greene
Bill Greene 2013-8-16

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Hi,
Yes, PDE Toolbox allows the BC (or PDE) coefficients to be imaginary. Are you running into a particular problem?
Bill
Simon
Simon 2013-8-17

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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!
Simon
Simon 2013-8-19

0 个投票

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

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