Calculation of 4 parameters

ρ

0

m

τ

and

c

of Cole-Cole model by complex rock core resistivity data measured with multi-frequency is an important nonlinear optimization problem in rock core complex resistivity experiments. However

in Jiaoshiba Zone

a very small

τ

and

c

with big value range cause the difficulty of the convergence of optimization program. Therefore

the initial value determination and optimized iteration step have been studied. The improved program performances well on the speed of convergence

and avoids the calculation failure caused by out-range of the parameter

τ

. The study indicates that accordin

g to the maximum property and asymmetry property

the parameter

τ

can be obtained directly

and good iteration initial values of the rest 3 parameters can be obtained either. Meanwhile

by transforming the error function to be Tyler series

the optimized iteration step can be obtained and the convergence speed can be upgraded significantly.