A field-theoretic description of the critical dynamics of spin systems
is constructed. Using the Padi-Borel summation technique, the dynamic
critical exponent for two-and three-dimensional systems is evaluated
directly in the four-loop approximation. The results are compared with
the values obtained for the dynamic exponent by Monte Carlo methods.
(C) 1997 American Institute of Physics. [S0021-3640(97)00924-9].