Renormgroup Invariants and Approximations of Mappings
  The relationship between mappings of sets and renormalization group transformations is established, and renormalization group invariants of such mappings are found. These results are valid both for continuous and discrete mappings and for various dimensionality of image and preimage of the mappings too. It is suggested a number of mapping approximations improved in comparison with an ordinary power expansion. The approximations take into account the global one-to-one character of the mappings. The method is illustrated by a number of examples: by reconstructing of some analytical functions, calculating the integral of the typical partition function of statistical mechanics and the ground state energy for the quartic anharmonic oscillator. In the whole range of nonlinearity parameter varying from zero up to infinity the accuracy of the RG approximation based on a few terms of divergent series is about 0.06% in the next to last case and 0.004% in the last one. 
Gennady N. Nikolaev