Solution
= Solution
The <Kronecker delta> restricts the <Einstein summation convention> to equal indices, giving the <dot product>
$$
\delta_{ij}a_ib_j=\sum_i a_ib_i=\boxed{\mathbf a\cdot\mathbf b}.
$$
= Solution
The <Kronecker delta> restricts the <Einstein summation convention> to equal indices, giving the <dot product>
$$
\delta_{ij}a_ib_j=\sum_i a_ib_i=\boxed{\mathbf a\cdot\mathbf b}.
$$