SRC/cpftri.f(3)

NAME
SRC/cpftri.f

SYNOPSIS

  Functions/Subroutines
subroutine cpftri (transr, uplo, n, a, info)
CPFTRI

Function/Subroutine Documentation

  subroutine cpftri (character transr, character uplo, integer n, complex, dimension( 0: * ) a, integer info)

CPFTRI

Purpose:

     CPFTRI computes the inverse of a complex Hermitian positive definite
     matrix A using the Cholesky factorization A = U**H*U or A = L*L**H
     computed by CPFTRF.

Parameters
    TRANSR

              TRANSR is CHARACTER*1
              = 'N':  The Normal TRANSR of RFP A is stored;
              = 'C':  The Conjugate-transpose TRANSR of RFP A is stored.

    UPLO

              UPLO is CHARACTER*1
              = 'U':  Upper triangle of A is stored;
              = 'L':  Lower triangle of A is stored.

    N

              N is INTEGER
              The order of the matrix A.  N >= 0.

    A

              A is COMPLEX array, dimension ( N*(N+1)/2 );
              On entry, the Hermitian matrix A in RFP format. RFP format is
              described by TRANSR, UPLO, and N as follows: If TRANSR = 'N'
              then RFP A is (0:N,0:k-1) when N is even; k=N/2. RFP A is
              (0:N-1,0:k) when N is odd; k=N/2. IF TRANSR = 'C' then RFP is
              the Conjugate-transpose of RFP A as defined when
              TRANSR = 'N'. The contents of RFP A are defined by UPLO as
              follows: If UPLO = 'U' the RFP A contains the nt elements of
              upper packed A. If UPLO = 'L' the RFP A contains the elements
              of lower packed A. The LDA of RFP A is (N+1)/2 when TRANSR =
              'C'. When TRANSR is 'N' the LDA is N+1 when N is even and N
              is odd. See the Note below for more details.
              On exit, the Hermitian inverse of the original matrix, in the
              same storage format.

    INFO

              INFO is INTEGER
              = 0:  successful exit
              < 0:  if INFO = -i, the i-th argument had an illegal value
              > 0:  if INFO = i, the (i,i) element of the factor U or L is
                    zero, and the inverse could not be computed.

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

      We first consider Standard Packed Format when N is even.
      We give an example where N = 6.
          AP is Upper             AP is Lower
       00 01 02 03 04 05       00
          11 12 13 14 15       10 11
             22 23 24 25       20 21 22
                33 34 35       30 31 32 33
                   44 45       40 41 42 43 44
                      55       50 51 52 53 54 55
      Let TRANSR = 'N'. RFP holds AP as follows:
      For UPLO = 'U' the upper trapezoid A(0:5,0:2) consists of the last
      three columns of AP upper. The lower triangle A(4:6,0:2) consists of
      conjugate-transpose of the first three columns of AP upper.
      For UPLO = 'L' the lower trapezoid A(1:6,0:2) consists of the first
      three columns of AP lower. The upper triangle A(0:2,0:2) consists of
      conjugate-transpose of the last three columns of AP lower.
      To denote conjugate we place -- above the element. This covers the
      case N even and TRANSR = 'N'.
             RFP A                   RFP A
                                    -- -- --
            03 04 05                33 43 53
                                       -- --
            13 14 15                00 44 54
                                          --
            23 24 25                10 11 55
            33 34 35                20 21 22
            --
            00 44 45                30 31 32
            -- --
            01 11 55                40 41 42
            -- -- --
            02 12 22                50 51 52
      Now let TRANSR = 'C'. RFP A in both UPLO cases is just the conjugate-
      transpose of RFP A above. One therefore gets:
               RFP A                   RFP A
         -- -- -- --                -- -- -- -- -- --
         03 13 23 33 00 01 02    33 00 10 20 30 40 50
         -- -- -- -- --                -- -- -- -- --
         04 14 24 34 44 11 12    43 44 11 21 31 41 51
         -- -- -- -- -- --                -- -- -- --
         05 15 25 35 45 55 22    53 54 55 22 32 42 52
      We next  consider Standard Packed Format when N is odd.
      We give an example where N = 5.
         AP is Upper                 AP is Lower
       00 01 02 03 04              00
          11 12 13 14              10 11
             22 23 24              20 21 22
                33 34              30 31 32 33
                   44              40 41 42 43 44
      Let TRANSR = 'N'. RFP holds AP as follows:
      For UPLO = 'U' the upper trapezoid A(0:4,0:2) consists of the last
      three columns of AP upper. The lower triangle A(3:4,0:1) consists of
      conjugate-transpose of the first two   columns of AP upper.
      For UPLO = 'L' the lower trapezoid A(0:4,0:2) consists of the first
      three columns of AP lower. The upper triangle A(0:1,1:2) consists of
      conjugate-transpose of the last two   columns of AP lower.
      To denote conjugate we place -- above the element. This covers the
      case N odd  and TRANSR = 'N'.
             RFP A                   RFP A
                                       -- --
            02 03 04                00 33 43
                                          --
            12 13 14                10 11 44
            22 23 24                20 21 22
            --
            00 33 34                30 31 32
            -- --
            01 11 44                40 41 42
      Now let TRANSR = 'C'. RFP A in both UPLO cases is just the conjugate-
      transpose of RFP A above. One therefore gets:
               RFP A                   RFP A
         -- -- --                   -- -- -- -- -- --
         02 12 22 00 01             00 10 20 30 40 50
         -- -- -- --                   -- -- -- -- --
         03 13 23 33 11             33 11 21 31 41 51
         -- -- -- -- --                   -- -- -- --
         04 14 24 34 44             43 44 22 32 42 52

Definition at line 211 of file cpftri.f.

Author

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