I saw the ADS press release concerning their harmonic balance simulator now working much better for highly nonlinear circuits.
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http://www.eetimes.com/news/design/showArticle.jhtml?articleID=180203235

Is anyone familiar with this method and what they may have done to improve their simulation capability?  They claim to also be able to do frequency dividers, but I am very interested in their claims of improved convergence overall.