centers a Div structure
[xcentered,x_mean] = centering(x, (mean));
a matrix (n x q) or a Div structure
a mean vector calculated with other data, to be applied to x
mean_i is a vector (1 x q) ou (q x 1) or a Div structure
a Div structure centered with its own mean or with mean_i
xcentered.d is of dimensions (n x q)
the vector used for centering x
x_mean_o.d is of dimensions (q x 1)