Aliasing in UVINIT

[ivan-pi]

The V argument is passed as an array of size 1.

pdecheb/pdecheb/cset.f

Lines 1 to 11 in f429435

	SUBROUTINE CSET(NPDE,NPTS,U,X,OMEGA,DU,XBK,NEL,NPTL,XC,CCR,XBH,
	* IBK,DUTEM,V,NV)
	C***********************************************************************
	C FORTRAN FUNCTIONS USED: SIN COS .
	C***********************************************************************
	C .. Scalar Arguments ..
	INTEGER IBK, NEL, NPDE, NPTL, NPTS, NV
	C .. Array Arguments ..
	DOUBLE PRECISIONCCR(NPTL), DU(NPTL,NPTL), DUTEM(NPTL,NPTL),
	* OMEGA(NPTL,NPTL), U(NPDE,NPTS), V(1), X(NPTS),
	* XBH(IBK), XBK(IBK), XC(NPTL)

...

pdecheb/pdecheb/cset.f

Line 122 in f429435

CALL UVINIT(NPDE,NPTS,X,U,NV,V)

This can have some surprising effects, if NV = 0, but the solution array would be declared as Y(NPDE*NPTS + 1) in the calling program. Here's the initialization routine that exposes the issue:

SUBROUTINE UVINIT( NPDE, NPTS, X, U, NV, V)
IMPLICIT NONE
INTEGER :: NPDE, NPTS, NV
DOUBLE PRECISION :: X(NPTS), U(NPDE,NPTS), TIME, V(NV)
U(1,:) = 0
U(1,NPTS) = 1
V(1) = 0       ! <-- eliminates effect of previous line
END SUBROUTINE

In practice this should be flagged as an out-of-bounds violation (or produce a segfault).

[ivan-pi]

The problem is more obvious in INICHB where CSET gets called:

      NVST = NPDE*NPTS + 1
C ...
      IV = NPDE*NPTS
      IF (NV.GT.0) THEN
         IV = NVST
C ...
      END IF
      CALL CSET(NPDE,NPTS,U,WK(I6),WK,WK(I2),WK(I5),NEL,NPTL,WK(I4),
     *          WK(I12),XBK,IBK,WK(I3),U(IV),NV)

If NV = 0, the element U(IV) will be the alias for U(NPDE*NPTS) or U(1,NPTS) in the UVINIT routine.