C PSTRE3    SOURCE    PV        22/04/25    21:15:10     11344          
c---------------------------------------------------------------------
c
      SUBROUTINE PSTRE3 (SIGMA, SGPRI)
c
c=====================================================================
c                                                                    =
c   This routine calculates the eigen stress values of 3D            =
c   'sigma (6)' and puts the results in 'sgpri (3)'.                 =
c                                                                    =
c    Note:   sigma = (Sxx, Syy, Szz, Sxy, Sxz, Syz)                  =
c            sgpri = (S11, S22, S33)                                 =
c                                                                    =
c=====================================================================
      IMPLICIT REAL*8 (A-H,O-Z)
      IMPLICIT INTEGER(I-N)
      real*8    sigma (6), sgpri (3)
c
      c2=-SIGMA(1)-SIGMA(2)-SIGMA(3)
      c1= (SIGMA(1)*SIGMA(2)+SIGMA(2)*SIGMA(3)+SIGMA(3)*SIGMA(1))
     &   - SIGMA(5)**2 - SIGMA(4)**2 - SIGMA(6)**2
      c0=-2.*SIGMA(4)*SIGMA(5)*SIGMA(6) + SIGMA(1)*SIGMA(6)**2
     &   + SIGMA(2)*SIGMA(5)**2 + SIGMA(3)*SIGMA(4)**2
     &   - SIGMA(1)*SIGMA(2)*SIGMA(3)
      call degre3(c0,c1,c2,d1,XI1,d2,XI2,d3,XI3)

      sgpri (1) = D1
      sgpri (2) = D2
      sgpri (3) = D3

      return
      end