Extensive chaos in the Nikolaevskii model

We carry out a systematic study of a different type of chaos at onset ("sof t-mode turbulence") based on numerical integration of the simplest one-dime nsional model. The chaos is characterized by a smooth interplay of differen t spatial scales, with defect generation being unimportant. The Lyapunov ex ponents are calculated for several system sizes for fixed values of the con trol parameter epsilon. The Lyapunov dimension and the Kolmogorov-Sinai ent ropy are calculated and both shown to exhibit extensive and microextensive scaling. The distribution functional is shown to satisfy Gaussian statistic s at small wave numbers and small frequency.