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Economical Models for Functional Covariation - SAMSI

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Overview <strong>Functional</strong> PCA finite element basis Estimation Examples Extensions and discussion<br />

Tensor notation<br />

Computing functions, gradients and hessians <strong>for</strong><br />

multi-index objects like R(s, t), which has six indices, is<br />

made much easier by using tensor notation.<br />

Einstein summation notation specifies that there is<br />

summation over repeated indices.<br />

Repeated indices usually occur in subscript/superscript<br />

pairs, called covariant and contravariant indices,<br />

respectively.<br />

Thus, in tensor notation<br />

σ(s i , t j ) = c k1 l 1<br />

r k 1l 1 k 2 l 2<br />

(s i , t j )c k2 l 2

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