Hello, i want programming this stationary equation but i don’t know, how i can programming the right hand side of this equation

-\mu \Delta C + (u.\nabla)C = \sum \limits_{{i=1}}^N F_i(t)\delta(r-r_0)

C(x,0) = C_0

delta is the dirac mass

F_i is the energy of the source.

Someone can help me how i can programming the dirac mass with freefem???

Thank you.