fem2d_heat, a MATLAB code which applies the finite element method to solve a form of the time-dependent heat equation over an arbitrary triangulated region.
The computational region is initially unknown by the program. The user specifies it by preparing a file containing the coordinates of the nodes, and a file containing the indices of nodes that make up triangles that form a triangulation of the region.
Normally, the user does not type in this information by hand, but has a program fill in the nodes, and perhaps another program that constructs the triangulation. However, in the simplest case, the user might construct a very crude triangulation by hand, and have TRIANGULATION_REFINE refine it to something more reasonable.
For the following ridiculously small example:
10-11-12 |\ |\ | \ | \ 6 7 8 9 | \| \ 1-2--3--4-5the node file would be:
0.0 0.0 1.0 0.0 2.0 0.0 3.0 0.0 4.0 0.0 0.0 1.0 1.0 1.0 2.0 1.0 3.0 1.0 0.0 2.0 1.0 2.0 2.0 2.0and the element file would be
1 3 10 2 7 6 3 5 12 4 9 8 12 10 3 11 7 8
The program is set up to handle the time dependent heat equation with a right hand side function, and nonhomogeneous Dirichlet boundary conditions. The state variable U(T,X,Y) is then constrained by:
Ut - ( Uxx + Uyy ) + K(x,y,t) * U = F(x,y,t) in the region U = G(x,y,t) on the boundary U = H(x,y,t) at initial time TINIT.
To specify the right hand side function F(x,y,t), the linear coefficient K(x,y,t), the boundary condition function G(x,y,t), and the initial condition H(x,y,t), the user has to supply the functions,
The program writes out a file containing the solution value at every node. This file may be used to create contour plots of the solution.
fem2d_heat ( 'prefix' )where 'prefix' is the common input filename prefix:
The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.
fem2d_heat is available in a C++ version and a FORTRAN90 version and a MATLAB version.
triangulation_display, a MATLAB code which displays the nodes and elements of a triangulation on the MATLAB graphics screen;