# Quasi-nonllinear Time-dependent Problem

Asked by
Ted Kord

Hi

I'm attempting to solve the following problem (using the C++ interface):

du/dt - div grad u = f(u)

Due to the non-linearity associated with f(u), I am using the parameters at time t to calculate it thus avoiding the use of a nonlinear root-finding algorithm.

The problem I have is how to define f(u).

Say, f(u) is:

0.1/(1 + exp(u - 2) )

How do obtain the scalar value 'u' to pass as the argument to f(u) at every time step.

Thanks.

Ted

## Question information

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- DOLFIN Edit question

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- Johan Hake

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