Hello everybody!
I clearly understand how to solve a standard Poisson’s equation in FF++. But can anyone suggest me how to solve it having the Dirac delta function as a RHS? I’m pretty newbie with FF+ so I’d appreciate any help you can give.
Here is an example: FreeFem-sources/Laplace-RHS-Dirac.edp at master · FreeFem/FreeFem-sources · GitHub.
Thank you for suggestion! It really helped me
Dirac delta funtion is generally difficult to implement in FEM. I am inerested in your problem and how you will do it.
If I understand the example it is also an anser to my question about adding
things without an integration 
Apparently and correct me if wrong the b term
in the example avoids the need to specify an “int2d” for example. For singular
stuff, my first reaction is fourier/laplace reciprocal space. Since the weak form
has an inherent integration step integrabe singularities I guess can take
care of themselves if you can do it yourself. With long ranges things,
say 1/r^n, I guess you just do the integrals but end up with non-zero b
elements everywhere.