converts an entry into a Div structure
x_div = div(x,(i_labels,v_labels));
a matrix (n x q) or a Div structure
if x is a matrix,i_labels et v_labels are string vectors of dimensions (n x 1) and ( q x 1) containing the line and column labels of x respectively
a Div structure corresponding to a Tlist: typeof(x_div)='div' and containing the fields: .d, .i and .v
x_div.d is a matrix or vector of numerical data of dimensions (n x q); the observations are set in lines and the variables in columns
x_div.i is a string vector of dimensions (n x 1) containing the labels of the observations (names, codes,...); by default: ['i1';'i2';...'in']
x_div.v is a string vector of dimensions (q x 1) containing the labels of the variables (wavelengths, names,...); by default: ['v1';'v2';...'vq']