Let

be a domain with smooth domain in

with

. Let
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(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
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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.