Cadabra manual: Diagonal

Diagonal

Declares a tensor to only have non-zero diagonal entries.

Indicates that the object to which the property is attached only has non-zero components on the diagonal, i.e. when all indices take the same value.

\delta_{m n}::Diagonal; ex:= \delta_{1 2} \delta_{1 2} - \delta_{1 1} \delta_{2 2};

\(\displaystyle{}\text{Attached property Diagonal to }{\delta}_(mn).\)

\(\displaystyle{}\delta_{1 2} \delta_{1 2}-\delta_{1 1} \delta_{2 2}\)

canonicalise(_);

\(\displaystyle{}-\delta_{1 1} \delta_{2 2}\)