The study of the Dirichlet problem with arbitrary measurable data
for harmonic functions is due to the famous dissertation of Luzin.
Later on, the known monograph of Vekua has been devoted to boundary
value problems (only with H\"older continuous data) for the
generalized analytic functions, i.e., continuous complex valued
functions $h(z)$ of the complex variable $z=x+iy$ with generalized
first partial derivatives by Sobolev satisfying equations of the
form $\partial_{\bar z}h\, +\, ah\, +\ bh\, =\, c\, ,$ where
$\partial_{\bar z}\ :=\ \frac{1}{2}\left(\ \frac{\partial}{\partial
x}\ +\ i\cdot\frac{\partial}{\partial y}\ \right),$ and it was
assumed that the complex valued functions $a,b$ and $c$ belong to
the class $L^{p}$ with some $p>2$ in the corresponding domains
$D\subset \mathbb C$. The present paper is a natural continuation of
our articles on the Riemann, Hilbert, Dirichlet, Poincare and, in
particular, Neumann boundary value problems for quasiconformal,
analytic, harmonic and the so-called $A-$harmonic functions with
boundary data that are measurable with respect to logarithmic
capacity. Here we extend the correspon\-ding results to the
generalized analytic functions $h:D\to\mathbb C$ with the sources
$g$ : $\partial_{\bar z}h\ =\ g\in L^p$, $p>2\,$, and to generalized
harmonic functions $U$ with sources $G$ : $\triangle\, U=G\in L^p$,
$p>2\,$. It was also given relevant definitions and necessary
references to the mentioned articles and comments on previous
results. This paper contains various theorems on the existence of
nonclassical solutions of the Riemann and Hilbert boundary value
problems with arbitrary measurable (with respect to logarithmic
capacity) data for generalized analytic functions with sources. Our
approach is based on the geometric (theoretic-functional)
interpretation of boundary values in comparison with the classical
operator approach in PDE. On this basis, it is established the
corresponding existence theorems for the Poincare problem on
directional derivatives and, in particular, for the Neumann problem
to the Poisson equations $\triangle\, U=G$ with arbitrary boundary
data that are measurable with respect to logarithmic capacity. These
results can be also applied to semi-linear equations of mathematical
physics in anisotropic and inhomogeneous media.