Integral Operator is Linear
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Theorem
Let $T$ be an integral operator.
Let $f$ and $g$ be integrable real functions on a domain appropriate to $T$.
Then $T$ is a linear operator:
- $\forall \alpha, \beta \in \R: \map T {\alpha f + \beta g} = \alpha \map T f + \beta \map T g$
Corollary 1
- $\forall \alpha, \beta \in \R: \map T {f + g} = \map T f + \map T g$
Corollary 2
- $\forall \alpha \in \R: \map T {\alpha f} = \alpha \map T f$
Proof
Let $T$ be expressed in its full form as an integral fransform:
- $\map T f := \ds \int_a^b \map f x \map K {p, x} \rd x$
for some integrable function $\map K {p, x}$.
Then:
\(\ds \map T {\alpha f + \beta g}\) | \(=\) | \(\ds \int_a^b \paren {\alpha \map f x + \beta \map g x} \map K {p, x} \rd x\) | ||||||||||||
\(\ds \) | \(=\) | \(\ds \int_a^b \paren {\alpha \map f x \map K {p, x} + \beta \map g x \map K {p, x} } \rd x\) | Real Multiplication Distributes over Addition | |||||||||||
\(\ds \) | \(=\) | \(\ds \alpha \int_a^b \map f x \map K {p, x} \rd x + \beta \int_a^b \map g x \map K {p, x} \rd x\) | Linear Combination of Definite Integrals | |||||||||||
\(\ds \) | \(=\) | \(\ds \alpha \map T f + \beta \, \map T g\) | Definition of Integral Operator |
$\blacksquare$