简介：IntheEasyDynmultibodyopensourceproject,computeralgebrahasbeenusedfromthebeginningtogeneratetheexpressionsofvelocitiesandaccelerationsofthebodies,bysymbolicdifferentiationoftheirposition.Originally,theMuPADcomputeralgebrasystemhadbeenretainedbecauseitwasfreelyavailablefornoncommercialpurposesandshowedverygoodtechnicalfeatures.Unfortunately,MuPADisnowadaysonlyavailablethroughcommercialchannelsandneedstobereplacedtokeepEasyDynpubliclyavailable.ThispaperpresentswhyXcas/Giacisfinallyselected,amongotherlong-termpromisingprojectslikeAxiom,Maxima,SageorYacas.Amongthechoicecriteria,theaccessibility,theportability,theeaseofuse,theautomaticexporttoClanguage,andthesimilaritywiththeMuPADlanguageareallconsidered.TheperformancesoftheMuPADandXcas/Giacimplementationsarealsocomparedonsomeexamples.