n-channel polynomial interpolation engine (nPINT), inspired by Francois Lekien, Chad Coulliette and Jerry Marsden, authors of "Tricubic interpolation in three dimensions" and "Tricubic Engine Technical Notes and Full Matrix".

create new nPINT object parameter hash structure:

{'pda' => [polynomial_degree_array], 'coef' => [nPINT_coefficients]}

the polynomial_degree_array contains the polynomial degree for each input channel, e.g. [3, 3, 3, 3] => 4 channels, each of degree 3

the nPINT coefficients define the behavior of the model. they are normally obtained using the 'fit' method, which uses linear least squares to fit the model to the supplied data. the number of rows in the coefficient array is equal to the product of each channel's degree + 1, e.g. if the pda is [3, 3, 3, 3], there are 256 coefficient rows. the number columns in the coefficient array is equal to the number of output channels.