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3.1 FDEs with Variable Coefficients     continued...

In the steady state limit, flow through a composite medium (a medium with a jump discontinuity in ) is determined by a harmonic average. See Exercise 5.

For implicit finite difference methods involving the flux at time , it is common practice to lag the -values by evaluating them using the U-values from time . The alternative is to deal with a system of algebraically nonlinear difference equations using some iterative procedure such as Newton's method for systems of equations.