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Park City Lectures on Eigenfunctions, Lecture 5: Lp norms of ...

Park City Lectures on Eigenfunctions, Lecture 5: Lp norms of ...

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Spectral projecti<strong>on</strong>s kernel = z<strong>on</strong>al harm<strong>on</strong>ic<br />

A key object in the theory <strong>of</strong> spherical harm<strong>on</strong>ics is the orthog<strong>on</strong>al<br />

projector<br />

Π k : L 2 (S 2 ) → H k .<br />

It has a kernel Π k (x, y) defined by<br />

∫<br />

Π k f (x) = Π k (x, y)f (y)dS(y).<br />

S n<br />

If {Y k m} is an orth<strong>on</strong>ormal basis <strong>of</strong> H k then<br />

d k<br />

∑<br />

Π k (x, y) = Ym(x)Y k m(y). k<br />

j=1

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