# Getting problem to compute order of convergence in Poisson eqn when exact solution in unknown

Here, i am sharing my codes. Please help if anyone know. Moreover, I want to do simulation on this codes. How to do simulation on this code so that i can see my solution how simulate at different time??.
poisson.edp (1.7 KB)

I sorry , but I do not understand what you want . You have no time in your equation so different time is no clean.

But please tell how i ger different L2-error so that i can compute order of convergence. I am getting same L2-error in every mesh size. Solution is uknown i want to compute L2-error and order of convergence. Please tell that i part. Thanks

No problem, because in you cas we know de exact solution

the corrected script:

poisson.edp (1.9 KB)

real ccc= 2./(2pi^2);
func uexact = ccc
sin(pix)sin(piy);
func Lapuexact= - ccc
2pi^2sin(pi*x)sin(piy);

Sir, why you using this, i don’t know eaxct solution then i want compute L2-error and order of convergence. That is, i want to compute L^2-error and order of convergence without using exact solution.
Suppose i don’t know the exact solution then, i want to compute L^2-error and order of convergence . Infact in lastly, you are setting uhold=ueaxct Which is eaxctly means i know eaxct solution. But this i not want sir. I want that i know only f and u=0 boundary then compute L^2-error and order of convergence.

I sorry, I you do no know the exact solution you car try to computation a good approximation on very very fine mesh, and use this solution as like an exact solution.

My way:
poisson-comp-fine-sol.edp (1.0 KB)