# DIFFUSION TOMS866 / IFISS Files for the Convection-Diffusion Equation

DIFFUSION is a directory of MATLAB M-files which are specifically for the solution of the diffusion equation, also known as the Poisson equation.

### Author:

• Howard Elman,
Department of Computer Science,
University of Maryland,
College Park, Maryland 20742,
USA,
elman@cs.umd.edu
• Alison Ramage,
Department of Mathematics,
University of Strathclyde,
26 Richmond Street,
Glasgow G1 1XH,
United Kingdom,
a.ramage@strath.ac.uk
• David Silvester,
School of Mathematics,
University of Manchester,
Sackville Street,
Manchester M60 1QD,
United Kingdom,
na.silvester@na-net.ornl.gov

### Source Code:

• deriv.m evaluates derivatives of bilinear shape functions.
• diffpost_bc.m postprocesses local Poisson error estimator.
• diffpost_p.m computes local Poisson error estimator for Q1 solution.
• diffpost_res.m computes Q1 element residual error estimator.
• ell_diff.m solve Poisson problem in L-shaped domain.
• femq1_diff.m vectorized bilinear coefficient matrix generator.
• femq2_diff.m vectorized biquadratic coefficient matrix generator.
• gauss_source.m evaluates source term at Gauss point.
• helpme_diff.m diffusion problem interactive help.
• lderiv.m evaluates derivatives of linear shape functions.
• localbc_p.m imposes Dirichlet BC for Poisson error estimator.
• lshape.m evaluates linear shape functions.
• nonzerobc.m imposes Dirichlet boundary condition.
• q1fluxjmps.m computes flux jumps for rectangular Q1 grid.
• q1res_diff.m computes interior residuals for rectangular Q1 grid.
• qderiv.m evaluates derivatives of biquadratic shape functions.
• qshape.m evaluates biquadratic shape functions.
• shape.m evaluates bilinear shape functions.
• specific_bc.m (current) problem boundary condition.
• specific_rhs.m (current) problem forcing function.
• square_diff.m solve Poisson problem in unit square domain.

### Subdirectories:

You can go up one level to the TOMS866 page.