I have a non-linear diffusion equation of the form

du/dt = \nabla.( D(u) \grad u) 

The non-linearity appears because of the dependence of the diffusion 
coefficient on the solution.

When discretising by the Rothe method, applying backward Euler method in 
the strictest sense:

(u^n - u^{n-1})/k^n  - \nabla. ( D(u^n) ) * \grad{u^n})  = 0

This would require Newton iterations and such complications.  Is it okay to 
simply use the numerical value of D from the previous time-step?

(u^n - u^{n-1})/k^n  - \nabla. ( D(u^{n-1}) ) * \grad{u^n})  = 0

In this case, we get a nice linear equation, and most of step-26 can be 
used as.  D(u) is a continuous function of u. Is this semi-explicit type of 
usage of diffusion coefficient, a reasonable way to tackle this problem?


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