Very simple question about differential equations, but I couldn't find anything online.
Let $f(x,z)$ be a function of two variables that satisfies:
$af+bf_x+cf_z+df_{xx}+ef_{zz}+gf_{xz}=q(x,z)$
where $q(x,z)$ is some known function, $a,b,c,d,e,g$ are constants.
How can I solve this, i.e., find an expression for $f(x,z)$ (given boundary conditions)?
Is there some reference where I can find general solution to differential equations of functions of two variables?