poisson, a MATLAB program which computes an approximate solution to the Poisson equation in a rectangular region.
The version of Poisson's equation being solved here is
- ( d/dx d/dx + d/dy d/dy ) U(x,y) = F(x,y)
over the rectangle 0 <= X <= 1, 0 <= Y <= 1, with exact solution
U(x,y) = sin ( pi * x * y )
so that
F(x,y) = pi^2 * ( x^2 + y^2 ) * sin ( pi * x * y )
and with Dirichlet boundary conditions along the lines x = 0, x = 1,
y = 0 and y = 1. (The boundary conditions will actually be zero in
this case, but we write up the problem as though we didn't know that,
which makes it easy to change the problem later.)
We compute an approximate solution by discretizing the geometry, assuming that DX = DY, and approximating the Poisson operator by
( U(i-1,j) + U(i+1,j) + U(i,j-1) + U(i,j+1) - 4*U(i,j) ) / dx /dy
Along with the boundary conditions at the boundary nodes, we have
a linear system for U. We can apply the Jacobi iteration to estimate
the solution to the linear system.
poisson is intended as a starting point for the implementation of a parallel version, using, for instance, MPI.
The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.
poisson is available in a C version and a C++ version and a FORTRAN90 version and a MATLAB version.
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