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integration and complex numbers
Posted 30 août 2011, 19:09 UTC−4 Low-Frequency Electromagnetics Version 4.1, Version 4.2 3 Replies
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I am using comsol 4.2 with the AC/DC module (more specific the electric currents).
I have a 3D bloc, with electric insulation everywhere.
electrical conductivity is 0.1+0.01i (yes it's a complex number).
permittivity is 1.
Two point sources, one acts as source +1 A, and one as sink -1A.
I changed the default solver to GMRES (so it can handle complex numbers).
My results (potential, current density,...) are now complex numbers.
My problem is when I integrate the current density, it gives me a real number. This happens only with the current desity. If I integrate potential or Electric field, I get complex results. How is this possible?
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I'm not sure why, not obvious to give a quick reply,
but you could check the underlying equation in COMSOL in the Equation view (see preferences)
There might be an issue with a simple or a complex conjugate multiplication, somewhere.
Check also the doc and the use of the operator "realdot()" with complex variables
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Good luck
Ivar
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I don't seem to find out why is that.
e.g.
Jx=ec.Jex+ec.Jix
Where in my case ec.Jex=0
Now ec.
Jix=ec.sigmaxx*ec.cucn1.input.Ex+ec.sigmaxy*ec.cucn1.input.Ey+ec.sigmaxz*ec.cucn1.input.Ez
Where ec.sigmaxx is a complex number
and ec.cunc1.Ex=-Vx which is a complex number.
Now if integrate ec.sigmaxx, I get a complex number (0.0102+0.001i)
integration of ec.cunc1.input.Ex=ec.Ex=-0.7723+0.0772i
bur integration of ec.sigmaxx*ec.Ex is a real number !!!
P.S.
Multiplication of ec.sigmaxx*ec.Ex = -0.080+(1.5e-5)i .
Can this be do to the number of decimical shown on comsol?
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from my understanding COMSOL uses double precision, try to see the size of the defined variable "eps" smallest number to substract from "1" to differentiate the result from "1"
Now what about integration, I'm not sure it integrates correctly without that the user separates the real and complex parts specifically.
You need to look into the doc again (or try it out experimentally) I'm in the same situation, cannot remember, shuld though ;)
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Good luck
Ivar