SUBROUTINE KESHCV(P4, SIGS, VP, MVP)
 
C  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
C   Convert errors in E, theta and phi for photons to a 3x3 covariance
C   matrix for Px, Py, Pz.
C
C  P4        real array (read)
C            4 vector of photon
C
C  SIGS      real array (read)
C            Errors in E, theta, phi
C
C *VP        real array (read)
C            4x4 covariance matrix
C
C  MVP       real array (read)
C            First dimension of VP
C  >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>