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diff --git a/Trivac/src/VALU4B.f b/Trivac/src/VALU4B.f
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+*DECK VALU4B
+      SUBROUTINE VALU4B(IELEM,NUN,LX,LY,X,Y,XXX,YYY,EVECT,ISS,KFLX,
+     + IXLG,IYLG,AXY)
+*
+*-----------------------------------------------------------------------
+*
+*Purpose:
+* Interpolate the flux distribution for DUAL method in 2D.
+*
+*Copyright:
+* Copyright (C) 2002 Ecole Polytechnique de Montreal
+* This library is free software; you can redistribute it and/or
+* modify it under the terms of the GNU Lesser General Public
+* License as published by the Free Software Foundation; either
+* version 2.1 of the License, or (at your option) any later version
+*
+*Author(s): R. Chambon
+*
+*Parameters: input
+* IELEM   finite element order
+*         =1 : linear Raviart-Thomas
+*         =2 : parabolic Raviart-Thomas
+*         =3 : cubic Raviart-Thomas
+*         =4 : quartic Raviart-Thomas
+* NUN     number of unknowns
+* LX      number of elements along the X axis.
+* LY      number of elements along the Y axis.
+* X       Cartesian coordinates along the X axis where the flux is
+*         interpolated.
+* Y       Cartesian coordinates along the Y axis where the flux is
+*         interpolated.
+* XXX     Cartesian coordinates along the X axis.
+* YYY     Cartesian coordinates along the Y axis.
+* EVECT   variational coefficients of the flux.
+* ISS     mixture index assigned to each element.
+* KFLX    correspondence between local and global numbering.
+* IXLG    number of interpolated points according to X.
+* IYLG    number of interpolated points according to Y.
+*
+*Parameters: output
+* AXY     interpolated fluxes.
+*
+*----------------------------------------------------------------------
+*
+      IMPLICIT NONE
+*----
+*  SUBROUTINE ARGUMENTS
+*----
+      INTEGER IELEM,NUN,LX,LY,IXLG,IYLG,ISS(LX*LY),KFLX(LX*LY)
+      REAL X(IXLG),Y(IYLG),XXX(LX+1),YYY(LY+1),EVECT(NUN),AXY(IXLG,IYLG)
+*----
+*  LOCAL VARIABLES
+*----
+      INTEGER I,J,L,IS,JS,IEL,I1,I2,IE
+      REAL ORDO,ABSC,COEF(2,5),FLX(5),FLY(5)
+      REAL U,V
+*----
+*  compute coefficient for legendre polynomials
+*----
+      COEF(:2,:5)=0.0
+      COEF(1,1)=1.0
+      COEF(1,2)=2.*3.**0.5
+      DO IE=1,3
+        COEF(1,IE+2)=2.0*REAL(2*IE+1)/REAL(IE+1)
+     1                     *(REAL(2*IE+3)/REAL(2*IE+1))**0.5
+        COEF(2,IE+2)=REAL(IE)/REAL(IE+1)
+     1                     *(REAL(2*IE+3)/REAL(2*IE-1))**0.5
+      ENDDO
+*----
+*  perform interpolation
+*----
+      DO 105 J=1,IYLG
+      ORDO=Y(J)
+      DO 100 I=1,IXLG
+      ABSC=X(I)
+      AXY(I,J)=0.0
+*
+*     Find the finite element index containing the interpolation point
+      IS=0
+      JS=0
+      DO 20 L=1,LX
+      IS=L
+      IF((ABSC.GE.XXX(L)).AND.(ABSC.LE.XXX(L+1))) GO TO 30
+   20 CONTINUE
+      CALL XABORT('VALU4B: WRONG INTERPOLATION(1).')
+   30 DO 40 L=1,LY
+      JS=L
+      IF((ORDO.GE.YYY(L)).AND.(ORDO.LE.YYY(L+1))) GO TO 70
+   40 CONTINUE
+      CALL XABORT('VALU4B: WRONG INTERPOLATION(2).')
+   70 IEL=(JS-1)*LX+IS
+*
+      IF(ISS(IEL).EQ.0) GO TO 100
+      U=(ABSC-0.5*(XXX(IS)+XXX(IS+1)))/(XXX(IS+1)-XXX(IS))
+      FLX(1)=COEF(1,1)
+      FLX(2)=COEF(1,2)*U
+      V=(ORDO-0.5*(YYY(JS)+YYY(JS+1)))/(YYY(JS+1)-YYY(JS))
+      FLY(1)=COEF(1,1)
+      FLY(2)=COEF(1,2)*V
+      IF(IELEM.GE.2) THEN
+        DO IE=2,IELEM
+          FLX(IE+1)=FLX(IE)*U*COEF(1,IE+1)-FLX(IE-1)*COEF(2,IE+1)
+          FLY(IE+1)=FLY(IE)*V*COEF(1,IE+1)-FLY(IE-1)*COEF(2,IE+1)
+        ENDDO
+      ENDIF
+      DO 92 I2=1,IELEM
+      DO 91 I1=1,IELEM
+        L=(I2-1)*(IELEM)+I1
+        AXY(I,J)=AXY(I,J)+EVECT(KFLX(IEL)+L-1)*FLX(I1)*FLY(I2)
+   91 CONTINUE
+   92 CONTINUE
+  100 CONTINUE
+  105 CONTINUE
+      RETURN
+      END