Integral equation
In mathematical analysis, integral equations are equations in which an unknown function appears under an integral sign. In mathematical notation, integral equations may thus be expressed as being of the form: f ( x 1 , x 2 , x 3 , … , x n ; u ( x 1 , x 2 , x 3 , … , x n ) ; I 1 ( u ) , I 2 ( u ) , I 3 ( u ) , … , I m ( u ) ) = 0 {\displaystyle f(x_{1},x_{2},x_{3},\ldots ,x_{n};u(x_{1},x_{2},x_{3},\ldots ,x_{n});I^{1}(u),I^{2}(u),I^{3}(u),\ldots ,I^{m}(u))=0} where I i ( u ) {\displaystyle I^{i}(u)} is an integral operator acting on u.