How to include constraint for pdepe solution (e.g., u>0)

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Abedeh Abd 2016-10-3

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https://ww2.mathworks.cn/matlabcentral/answers/305542-how-to-include-constraint-for-pdepe-solution-e-g-u-0

评论： Abedeh Abd 2016-10-3

Hello, I want to solve a parabolic partial differential equation (i.e., mixed Richards' Eq): du/dt=d/dz(A(z)*du/dz+B(z)) I want to put a constraint so that all solution are greater than a constant value, c (u>c). I would be grateful if you help me.

Thanks, Abedeh

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Answer 1

Gareth Thomas 2016-10-3

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https://ww2.mathworks.cn/matlabcentral/answers/305542-how-to-include-constraint-for-pdepe-solution-e-g-u-0#answer_237121

Piecewise function

In R2016b one can use the Piecewise function. I hope that this helps you.

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Abedeh Abd 2016-10-3

Sorry! I did not get your hint. Would you please explain more. Assume I use pdepe and pdepe solve it (i.e., u). some elements of solution (u) is less than 0.05. However, I know u never is less than 0.05 in nature (physically basis). How should I define this constraint to pdepe? I do not want to manually change it using u(find(u<0.05))=0.05 after pdepe solve equation.

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