LAPACK 3.3.0

ssyswapr.f

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00001       SUBROUTINE SSYSWAPR( UPLO, N, A, I1, I2)
00002 *
00003 *  -- LAPACK auxiliary routine (version 3.3.0) --
00004 *  -- LAPACK is a software package provided by Univ. of Tennessee,    --
00005 *  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
00006 *     November 2010
00007 *
00008 *     .. Scalar Arguments ..
00009       CHARACTER        UPLO
00010       INTEGER          I1, I2, N
00011 *     ..
00012 *     .. Array Arguments ..
00013       REAL             A(N,N)
00014 *
00015 *  Purpose
00016 *  =======
00017 *
00018 *  SSYSWAPR applies an elementary permutation on the rows and the columns of
00019 *  a symmetric matrix.
00020 *
00021 *  Arguments
00022 *  =========
00023 *
00024 *  UPLO    (input) CHARACTER*1
00025 *          Specifies whether the details of the factorization are stored
00026 *          as an upper or lower triangular matrix.
00027 *          = 'U':  Upper triangular, form is A = U*D*U**T;
00028 *          = 'L':  Lower triangular, form is A = L*D*L**T.
00029 *
00030 *  N       (input) INTEGER
00031 *          The order of the matrix A.  N >= 0.
00032 *
00033 *  A       (input/output) REAL array, dimension (LDA,N)
00034 *          On entry, the NB diagonal matrix D and the multipliers
00035 *          used to obtain the factor U or L as computed by SSYTRF.
00036 *
00037 *          On exit, if INFO = 0, the (symmetric) inverse of the original
00038 *          matrix.  If UPLO = 'U', the upper triangular part of the
00039 *          inverse is formed and the part of A below the diagonal is not
00040 *          referenced; if UPLO = 'L' the lower triangular part of the
00041 *          inverse is formed and the part of A above the diagonal is
00042 *          not referenced.
00043 *
00044 *  I1      (input) INTEGER
00045 *          Index of the first row to swap
00046 *
00047 *  I2      (input) INTEGER
00048 *          Index of the second row to swap
00049 *
00050 *  =====================================================================
00051 *
00052 *     ..
00053 *     .. Local Scalars ..
00054       LOGICAL            UPPER
00055       INTEGER            I
00056       REAL               TMP
00057 *
00058 *     .. External Functions ..
00059       LOGICAL            LSAME
00060       EXTERNAL           LSAME
00061 *     ..
00062 *     .. External Subroutines ..
00063       EXTERNAL           SSWAP
00064 *     ..
00065 *     .. Executable Statements ..
00066 *
00067       UPPER = LSAME( UPLO, 'U' )
00068       IF (UPPER) THEN
00069 *
00070 *         UPPER
00071 *         first swap
00072 *          - swap column I1 and I2 from I1 to I1-1 
00073          CALL SSWAP( I1-1, A(1,I1), 1, A(1,I2), 1 )
00074 *
00075 *          second swap :
00076 *          - swap A(I1,I1) and A(I2,I2)
00077 *          - swap row I1 from I1+1 to I2-1 with col I2 from I1+1 to I2-1     
00078          TMP=A(I1,I1)
00079          A(I1,I1)=A(I2,I2)
00080          A(I2,I2)=TMP
00081 *
00082          DO I=1,I2-I1-1
00083             TMP=A(I1,I1+I)
00084             A(I1,I1+I)=A(I1+I,I2)
00085             A(I1+I,I2)=TMP
00086          END DO
00087 *
00088 *          third swap
00089 *          - swap row I1 and I2 from I2+1 to N
00090          DO I=I2+1,N
00091             TMP=A(I1,I)
00092             A(I1,I)=A(I2,I)
00093             A(I2,I)=TMP
00094          END DO
00095 *
00096         ELSE
00097 *
00098 *         LOWER
00099 *         first swap
00100 *          - swap row I1 and I2 from I1 to I1-1 
00101          CALL SSWAP( I1-1, A(I1,1), N, A(I2,1), N )
00102 *
00103 *         second swap :
00104 *          - swap A(I1,I1) and A(I2,I2)
00105 *          - swap col I1 from I1+1 to I2-1 with row I2 from I1+1 to I2-1     
00106           TMP=A(I1,I1)
00107           A(I1,I1)=A(I2,I2)
00108           A(I2,I2)=TMP
00109 *
00110           DO I=1,I2-I1-1
00111              TMP=A(I1+I,I1)
00112              A(I1+I,I1)=A(I2,I1+I)
00113              A(I2,I1+I)=TMP
00114           END DO
00115 *
00116 *         third swap
00117 *          - swap col I1 and I2 from I2+1 to N
00118           DO I=I2+1,N
00119              TMP=A(I,I1)
00120              A(I,I1)=A(I,I2)
00121              A(I,I2)=TMP
00122           END DO
00123 *
00124       ENDIF
00125       END SUBROUTINE SSYSWAPR
00126 
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