I ' msorryifthisquestionseemsareallybasic，buticannotfindagoodansweronlineyet。
I ' malittleconfusedwithvectorsandhowtousetheminmatlab.atthemomentihavethefollowingthreepairofcooordinates (:个人1，tthemome
nowiwanttocalculatetheanglebetween ' thevectorwhichgoesfromperson1to person2' and ' thevectorfromperson1to person1future '.ini hiswiththevectors，butiamnotsureiamactuallyusingtherightinputforeachvector。
sonowmyquestionishowcaniusethesecoordinates (andthedifferencebetweenthem ) tocalculatetheanglefromtheimage？
althoughstefanm ' ssolutionisaprettycommonsolutiontothis，itisactuallycomputationallyexpensive，but most importantly， incorrectwhenthevectorsaretinyand/ortheangleisnear0or--itcanactuallyresultinanglesthatareslightlynegative，orslightlyexexynegate
Thus，it gives a false sense of robustness。
I'd instead suggest
theta=ACOS(min(1，max(-1，a ) a(a(: ).' *b ) : )/FZDBM(a )/FZDBM(a ) ) ) ) ) )
More robust，more correct，over 10 faster when run in a loop，andunderstandablebysdwdwithoutdocumentation，becauseitststillagresmes