autopdex.models.kelvin_mandel_extract

autopdex.models.kelvin_mandel_extract(a)

Converts a 6-component Kelvin-Mandel representation vector into a 3x3 symmetric matrix.

In the Kelvin-Mandel notation, the off-diagonal components are scaled by 1/sqrt(2) to preserve norm equivalence between the tensor and its vector representation. This function extracts the full symmetric matrix from its compact vector representation.

Parameters:

a – 1-dimensional array-like with 6 elements corresponding to the Kelvin-Mandel representation of a 3x3 symmetric tensor. The expected ordering is: [a11, a22, a33, a12, a13, a23]

Returns:

A 3x3 jnp.ndarray representing the symmetric tensor in matrix form.