Wrong matrix for the tetragonal system?

[qzhu2017]

@jochym

I think there maybe something wrong with your code for the tetragonal systems.

def tetragonal(u):
    '''
    Equation matrix generation for the tetragonal lattice.
    The order of constants is as follows:
    .. math::
       C_{11}, C_{33}, C_{12}, C_{13}, C_{44}, C_{66}
    :param u: vector of deformations:
        [ :math:`u_{xx}, u_{yy}, u_{zz}, u_{yz}, u_{xz}, u_{xy}` ]
    :returns: Symmetry defined stress-strain equation matrix
    '''

    uxx, uyy, uzz, uyz, uxz, uxy = u[0], u[1], u[2], u[3], u[4], u[5]
    return array(
                [[uxx,   0,    uyy,  uzz,      0,      0],
                 [uyy,   0,    uxx,  uzz,      0,      0],
                 [0,     uzz,  0,    uxx+uyy,  0,      0],
                 [0,     0,    0,    0,        2*uyz,  0],
                 [0,     0,    0,    0,        2*uxz,  0],
                 [0,     0,    0,    0,        0,  2*uxy]])

Also, https://github.com/jochym/Elastic/blob/8daae37d0c48aab8dfb1de2839dab02314817f95/elastic/elastic.py#L297 The last independent elastic constant should be C_66 not C_14.

            4: ('C_11', 'C_33', 'C_12', 'C_13', 'C_44', 'C_66'), #error in the original code

Could you please check if my fix is correct?

Thanks,

[jochym]

You are right. The correct last component is indeed C66. Thanks @qzhu2017

[jochym]

Fixed in https://github.com/jochym/Elastic/commit/ec9cd7088ba13979d2ba032b42f238dbd9fa3931 and published in v5.2.1.