Let
be a domain with smooth domain in
with
. Let
(with sufficient regularity) represent the conductivity of the medium
. Given any sufficiently regular
(voltage), there exists a unique solution
of the conductivity equation
This equation is derived by the conservation law. The Calder\'{o}n problem asked whether the electrical conductivity
can be uniquely determined by making voltage
and current measurements
on its boundary
. In this talk, starting from the famous Calder\'{o}n problem, we will give an introduction to the inverse problem. Moreover, we will exhibit some recent results of some inverse problems.