[gorkemocalan]

Hi,

I have some problems about error analysis of Laplace Eqn. in 2D. I generated coefficient matrix and right-hand side vector as Au=b format properly and solved u=A\b.

I calculated analytical solution with respect to boundary conditions which are
u(x,0)=0 ,u(x,1)=x-x^2, u(0,y)=0, u(1,y)=0.

There is a problem about error. I was expecting to observe the decrease in error by making the mesh finer. But it did not happen in that way. 41x41 mesh gave better error result than 81x81 mesh.

I also attached the code (MATLAB) for the people who are interested in.

Thanks for your concern...

[FMDenaro]

indeed, the error must diminuish ... how do you invert A? check if A*A^-1 is the identity matrix (note that u=A^-1*b)
Check also the exact solution

[H0T_S0UP]

Be careful with MATLAB. Its matrix operations don't always work the way you'd expect.