(ed.). Gravitational waves (IOP, 2001)(422s).

400 Numerical relativityof Einstein’s equations, including the ADM formalism and the Bona–Massóhyperbolic formulation, can be chosen as input parameters, as can differentgauge conditions, horizon finders, hydrodynamics evolvers, etc. Cactus was alsodesigned as a community code. After first developing and testing it within ourrather large community of collaborators, it is available with full documentation.By having an entire research community using and contributing to such a code,we hope to accelerate the maturation of numerical relativity. Information aboutthe code is available online, and can be accessed at http://www.cactuscode.orgAcknowledgmentsIt is a pleasure to acknowledge many friends and colleagues who have contributedto the work described in this article, some of which was derived from papers wehave written together. I especially thank Wai-Mo Suen, who helped write previousreviews on which this article is partly based. The Cactus code was originallystarted by Joan Massó and Paul Walker at AEI. Without the contributions frompeople at many institutions, the work described here would not have beenpossible. This work has been supported by AEI, NCSA, NSF Grant No PHY-96-00507, NASA HPCC/ESS Grand Challenge Applications Grant No NCCS5-153and NSF MRAC Allocation Grant No MCA93S025.18.9 Further readingHere are some references that we think will help fill in the details of many issueswe can only gloss over. These references are clearly not complete; it was justeasier for us to heavily bias this list towards work coming out of our own group,or closely associated groups! Our apologies to many others who have written finepapers on these subjects, but we have tried to give references that are current andrelevant to the most important topics in numerical relativity, if incomplete andbiased.18.9.1 Overviews/formalisms of numerical relativityFor basic 3 + 1 formalism, see [10] and the PhD thesis of Cook [88]. Thisprovides the basics in a very clear, readable way. A somewhat more recent Yorkarticle describes many ‘miscellaneous’ topics, such as more modern initial dataand apparent horizon conditions, etc [20]. However, there are no details on morerecent reformulations of Einstein’s equations for numerical relativity, which arebecoming very important. This is a breaking research area, with new papers everymonth, but some that stand out for hyperbolicity are [32–34, 46, 52, 63, 70, 149,150, and references therein]. Even these are being overtaken by some recentdevelopments! Every month there is new excitement in some variations on all