;+ ;Function: qinv,q ; ;Purpose: calculate the inverse of a quaternion or an array of quaternions ; ;Inputs: q: a 4 element array, or an Nx4 element array, representing quaternion(s) ; ;Returns: q^-1 ; ;Notes: Implementation largely copied from the euve c library for ;quaternions ;Represention has q[0] = scalar component ; q[1] = vector x ; q[2] = vector y ; q[3] = vector z ; ;The vector component of the quaternion can also be thought of as ;an eigenvalue of the rotation the quaterion performs ; ; ;Written by: Patrick Cruce(pcruce@igpp.ucla.edu) ; ; ; $LastChangedBy: pcruce $ ; $LastChangedDate: 2007-11-11 17:12:08 -0800 (Sun, 11 Nov 2007) $ ; $LastChangedRevision: 2027 $ ; $URL: svn+ssh://thmsvn@ambrosia.ssl.berkeley.edu/repos/ssl_general/trunk/cotrans/cotrans.pro $ ;- function qinv,q compile_opt idl2 ;this is to avoid mutating the input variable qi = q ;check to make sure input has the correct dimensions qi = qvalidate(qi,'q','qinv') if(size(qi,/n_dim) eq 0 && qi[0] eq -1) then return,qi qc = qconj(qi) ;if conjugation fails if(size(qc,/n_dim) eq 0 && qc[0] eq -1) then return,qi qn = qnorm(qi) ;if norm fails if(size(qn,/n_dim) eq 0 && qn[0] eq -1) then return,qi if(qn eq 0) then begin dprint,'0 length quaternion has no inverse' return,-1 endif qn2=qn*qn qtmp0 = qc[*,0]/qn2 qtmp1 = qc[*,1]/qn2 qtmp2 = qc[*,2]/qn2 qtmp3 = qc[*,3]/qn2 qout = [[qtmp0],[qtmp1],[qtmp2],[qtmp3]] return,reform(qout) end