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PDE system - pdepe system example - error or incomplete description on Matlab website?

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Leonid on 19 Dec 2019
Commented: Bill Greene on 24 Dec 2019
I am no longer sure how to use Matlab's pdepe properly for solving a system of PDEs after checking the example given on Matlab's help website.
If you look to an example here under the 'Code Equation' you'll see a rewritten pde system in a matrix form. Comparing it to the original equation it is obvious that either the term " a*dndx*dcdx " is missing from the first (rewritten) equation, or Matlab implicity assumes that the derivative is acting only on the dudx terms when it deals with pde systems (this will be very weird). Could anyone with an extensive experiece in solving pde systems in Matlab clarify this?


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Accepted Answer

Bill Greene
Bill Greene on 20 Dec 2019
Looks like you have found an error in this documentation page. If you look at equation 3 in the referenced paper you will see that this equation corresponds to what is actually coded in the pdepe example. The results from the pdepe analysis agree with figures 3 and 4 in the referenced paper. It is the first PDE in the documentation page that is incorrect.


Leonid on 23 Dec 2019
Thanks for your answer. Based on the referenced paper it is the documentation page that contains error.
One additional thing that will be helpful to clarify:
If the coefficients d and a were functins of x [for example defined by some discrete data (and then interpolated within the function)], whould their derivatives through the flux term be taken into account by Matlab pdepe?

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