DTFTTR(3) copies a triangular matrix A from rectangular full packed format (TF) to standard full format (TR)

SYNOPSIS

SUBROUTINE DTFTTR(
TRANSR, UPLO, N, ARF, A, LDA, INFO )

    
CHARACTER TRANSR, UPLO

    
INTEGER INFO, N, LDA

    
DOUBLE PRECISION A( 0: LDA-1, 0: * ), ARF( 0: * )

PURPOSE

DTFTTR copies a triangular matrix A from rectangular full packed format (TF) to standard full format (TR).

ARGUMENTS

TRANSR (input) CHARACTER
= 'N': ARF is in Normal format;
= 'T': ARF is in Transpose format.
UPLO (input) CHARACTER

= 'U': A is upper triangular;
= 'L': A is lower triangular.
N (input) INTEGER
The order of the matrices ARF and A. N >= 0.
ARF (input) DOUBLE PRECISION array, dimension (N*(N+1)/2).
On entry, the upper (if UPLO = 'U') or lower (if UPLO = 'L') matrix A in RFP format. See the "Notes" below for more details.
A (output) DOUBLE PRECISION array, dimension (LDA,N)
On exit, the triangular matrix A. If UPLO = 'U', the leading N-by-N upper triangular part of the array A contains the upper triangular matrix, and the strictly lower triangular part of A is not referenced. If UPLO = 'L', the leading N-by-N lower triangular part of the array A contains the lower triangular matrix, and the strictly upper triangular part of A is not referenced.
LDA (input) INTEGER
The leading dimension of the array A. LDA >= max(1,N).
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value

FURTHER DETAILS

We first consider Rectangular Full Packed (RFP) 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 the 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 the transpose of the last three columns of AP lower.
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 = 'T'. RFP A in both UPLO cases is just the 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 first consider Rectangular Full Packed (RFP) 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 the 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 the transpose of the last two columns of AP lower.
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 = 'T'. RFP A in both UPLO cases is just the 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
Reference
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