a generalization of the concept of linear transformation to vector spaces. F is called a linear operator on a vector space E if it is a function on E with values in some vector space E1 and has the linearity property
F(αx + βy) = αF(x) + βF(y)
where x and y are elements of E, and α and β are numbers. If the E and E1 are normed spaces and ǀǀF(x)ǀǀ / ǀǀxǀǀ is uniformly bounded for all x ∈ E, then the linear operator F is said to be bounded and
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is called its norm.
The most important linear operators on function spaces are the differential linear operators
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and the integral linear operators
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The Laplace operator is an example of a linear operator on a space of functions of many variables. The theory of linear operators finds numerous applications in various problems of mathematical physics and applied mathematics.