TEvtGen/PHOTOS/photri.F

   1       FUNCTION PHOTRI(A,B,C)
   2 C.----------------------------------------------------------------------
   3 C.
   4 C.    PHOTOS:   PHOton radiation in decays calculation of TRIangle fie
   5 C.
   6 C.    Purpose:  Calculation of triangle function for phase space.
   7 C.
   8 C.    Input Parameters:  A, B, C (Virtual) particle masses.
   9 C.
  10 C.    Output Parameter:  Function value =
  11 C.                       SQRT(LAMBDA(A**2,B**2,C**2))/(2*A)
  12 C.
  13 C.    Author(s):  B. van Eijk                     Created at:  15/11/89
  14 C.                                                Last Update: 02/01/90
  15 C.
  16 C.----------------------------------------------------------------------
  17       IMPLICIT NONE
  18       DOUBLE PRECISION DA,DB,DC,DAPB,DAMB,DTRIAN
  19       REAL*8 A,B,C,PHOTRI
  20       DA=A
  21       DB=B
  22       DC=C
  23       DAPB=DA+DB
  24       DAMB=DA-DB
  25       DTRIAN=SQRT((DAMB-DC)*(DAPB+DC)*(DAMB+DC)*(DAPB-DC))
  26       PHOTRI=DTRIAN/(DA+DA)
  27       RETURN
  28       END