This function will take the sample Rs and return the
sample Rs centered at S, i.e. the returned sample is
$S^\top R$. If S is the true center then the
projected mean should be close to the 3-by-3 identity
matrix
Usage
center(x, S)
## S3 method for class 'SO3':
center(x, S)
## S3 method for class 'Q4':
center(x, S)
Arguments
x
$n\times p$ matrix where each row
corresponds to a random rotation in matrix (p=9) or
quaternion (p=4) form.