Calculate covariance matrix between individual landmark coordinates. Skips any missing values in computation of covariance matrix.
An N x 3 x M array where N is the number of landmarks, 3 is the number of dimensions, and M is the number of specimens.
This function does not guarantee that the returned matrix is
positive definite. If the covariance matrix is not positive definite
a warning is given and the matrix can be bent to create the closest
positive definite matrix with
3N x 3N covariance matrix