strttf (l) - Linux Man Pages

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

NAME

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

SYNOPSIS

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

    
CHARACTER TRANSR, UPLO

    
INTEGER INFO, N, LDA

    
REAL A( 0: LDA-1, 0: * ), ARF( 0: * )

PURPOSE

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

ARGUMENTS

TRANSR (input) CHARACTER
= aqNaq: ARF in Normal form is wanted;
= aqTaq: ARF in Transpose form is wanted.
UPLO (input) CHARACTER

= aqUaq: Upper triangle of A is stored;
= aqLaq: Lower triangle of A is stored.
N (input) INTEGER
The order of the matrix A. N >= 0.
A (input) REAL array, dimension (LDA,N).
On entry, the triangular matrix A. If UPLO = aqUaq, 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 = aqLaq, 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 matrix A. LDA >= max(1,N).
ARF (output) REAL array, dimension (NT).
NT=N*(N+1)/2. On exit, the triangular matrix A in RFP format.
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 = aqNaq. RFP holds AP as follows:
For UPLO = aqUaq 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 = aqLaq 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 = aqNaq.

 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 = aqTaq. 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 = aqNaq. RFP holds AP as follows:
For UPLO = aqUaq 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 = aqLaq 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 = aqNaq.

 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 = aqTaq. 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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