# MikeBattaglia's profile - activity

 2019-06-16 00:40:29 +0200 answered a question Series expansion for theta function of even lattice There is a simpler explanation, which is that the quadratic form [ 2 -1 ] [ * 2 ]  Maps to the matrix [ 2 -1 ] [ 0 2 ]  Which is equivalent to the symmetric matrix [2 -1/2] [-1/2 2]  Which can be gotten with A.Gram_matrix(). The A.matrix() function listed in the answer above is the Hessian, which is double the Gram matrix. The documentation for Gram matrix gives as an example a Quadratic form with diagonal matrix. Should probably be updated to include off-diagonal terms to make this clearer.