On hyperbolic summation and hyperbolic moduli of smoothness

This paper deals with the method of hyperbolic summation of tensor product orthogonal spline functions onI ^d. The spaces, defined in terms of the order of the best approximation by the elements of the space spanned by the tensor product functions with indices from a given hyperbolic set, are described both in terms of the coefficients in some basis and as interpolation spaces. Moreover, the hyperbolic modulus of smoothness is studied, and some relations between hyperbolic summation and hyperbolic modulus of smoothness are established.