Calculate the operator norm defined on L2
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Clash Royale CLAN TAG #URR8PPP up vote 1 down vote favorite For $f in L^2([0, 1]) $ and $x in [0, 1]$ we have the following $$ A(f)(x) = int_0^1 (x - y) f(y)dy $$ In this particular exercise I have to calculate the operator norm $| A |$. We know that from a theorem that if $A$ is compact and self-adjoint then either $|A|$ or $-| A |$ is an eigenvalue to the operator $A$. My attempt: We know that $A$ is indeed compact, but it is not self-adjoint. However, by some inspection, we have that $iA$ is self-adjoint (and compact). So we just have to calculate $|iA| = |A| = |lambda|$ where $lambda$ is an eigenvalue satisfying $A(f)(x) = lambda f(x)$, for some eigenfunction $f$. Now setting $f(x) = a + bx$ we get by calculation that $$lambda(a + bx) = int_0^1 (x - y) (a + by) dy = -frac a 2 - frac b 3 + (a + frac b 2)x.$$ But from this I'm not sure how to solve for $lambda$. Maybe there is an another way to solve this? functional-analysis share | cite | improve this questi...