The Monte Carlo method for conjugate stationary diffusion equation with special item

We consider the three-dimensional Dirichlet problem for the equation Δu + (v, grad u) + cu = -g, u|Γ = ψ in a domain Ω with the boundary Γ, which is assumed simply connected and piecewise smooth. We suppose the functions v, c, and g to satisfy the Hölder condition in Ω, and the function ψ to be continuous on Γ.