KALLOWED Function

    LOGICAL FUNCTION KALLOWED(G, NBASISMAX)
! See if a given G vector is within a (possibly tilted) unit cell.
! Used to generate the basis functions for the hubbard model (or perhaps electrons in boxes)
        Type(BasisFN), intent(in) :: G
        INTEGER nBasisMax(5, *), NMAXX, I, J, AX, AY
        INTEGER KX, KY
        real(dp) MX, MY, XX, YY
        LOGICAL TALLOW
        TALLOW = .TRUE.
        IF (NBASISMAX(3, 3) == 1) THEN
!.. spatial symmetries
            IF (G%k(1) /= 0) TALLOW = .FALSE.
        ELSEIF (NBASISMAX(3, 3) == 0) THEN
!.. Hubbard
            IF (NBASISMAX(1, 3) == 1) THEN
!.. Tilted hubbard
                NMAXX = NBASISMAX(1, 5)
!         NMAXY=
                AX = NBASISMAX(1, 4)
                AY = NBASISMAX(2, 4)
!.. (XX,YY) is the position of the bottom right corner of the unit cell
                XX = ((AX + AY) / 2.0_dp) * NMAXX
                YY = ((AY - AX) / 2.0_dp) * NMAXX
                MX = XX * AX + YY * AY
                MY = XX * AY - YY * AX
                I = G%k(1)
                J = G%k(2)
                KX = I * AX + J * AY
                KY = I * AY - J * AX
                IF (KX > MX) TALLOW = .FALSE.
                IF (KY > MY) TALLOW = .FALSE.
                IF (KX <= -MX) TALLOW = .FALSE.
                IF (KY <= -MY) TALLOW = .FALSE.
            ELSEIF (NBASISMAX(1, 3) >= 4 .OR. NBASISMAX(1, 3) == 2) THEN
!.. Real space Hubbard
                IF (G%k(1) == 0 .AND. G%k(2) == 0 .AND. G%k(3) == 0) THEN
                    TALLOW = .TRUE.
                ELSE
                    TALLOW = .FALSE.
                END IF
!      ELSEIF(NBASISMAX(1,3).EQ.2) THEN
!.. mom space non-pbc non-tilt hub - parity sym
!          IF(  (G(1).EQ.0.OR.G(1).EQ.1)
!     &       .AND.(G(2).EQ.0.OR.G(2).EQ.1)
!     &       .AND.(G(3).EQ.0.OR.G(3).EQ.1)) THEN
!              TALLOW=.TRUE.
!          ELSE
!              TALLOW=.FALSE.
!          ENDIF
!      ELSEIF(NBASISMAX(1,3).EQ.2) THEN
!.. non-pbc hubbard
!          TALLOW=.TRUE.
!          IF(G(1).GT.NBASISMAX(1,2).OR.G(1).LT.NBASISMAX(1,1))
!     &       TALLOW=.FALSE.
!          IF(G(2).GT.NBASISMAX(2,2).OR.G(2).LT.NBASISMAX(2,1))
!     &       TALLOW=.FALSE.
!          IF(G(3).GT.NBASISMAX(3,2).OR.G(3).LT.NBASISMAX(3,1))
!     &       TALLOW=.FALSE.
            ELSE
!.. Normal Hubbard
                TALLOW = .TRUE.
                IF (G%k(1) > NBASISMAX(1, 2) .OR. G%k(1) < NBASISMAX(1, 1)) TALLOW = .FALSE.
                IF (G%k(2) > NBASISMAX(2, 2) .OR. G%k(2) < NBASISMAX(2, 1)) TALLOW = .FALSE.
                IF (G%k(3) > NBASISMAX(3, 2) .OR. G%k(3) < NBASISMAX(3, 1)) TALLOW = .FALSE.
            END IF
        END IF
        KALLOWED = TALLOW
        RETURN
    END FUNCTION KALLOWED