eigenproblem of a special symmetric matrix

[klmn]

Dear Lapack developers and users,
I would be very grateful for your advice on the following problem.

My symmetric matrix is specified by two vectors a and b as:
a·a^T + diag(b), where diag(b) is a diagonal matrix with elements taken from b.

One can solve eigenproblem for this matrix by standard means.
But is there a more elegant way?