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LAPACK: Fix documentation error and ordering bug in DLASD7 #5344

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Merged
merged 2 commits into from
Jun 29, 2025
Merged

LAPACK: Fix documentation error and ordering bug in DLASD7 #5344

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0904a42
Fix documentation error and ordering bug in DLASD7
Jun 25, 2025
b37889e
Merge branch 'OpenMathLib:develop' into fix-dlasd7
MaartenBaert Jun 26, 2025
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13 changes: 10 additions & 3 deletions lapack-netlib/SRC/dlasd7.f
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Original file line number Diff line number Diff line change
Expand Up @@ -101,7 +101,7 @@
*> On entry D contains the singular values of the two submatrices
*> to be combined. On exit D contains the trailing (N-K) updated
*> singular values (those which were deflated) sorted into
*> increasing order.
*> decreasing order.
*> \endverbatim
*>
*> \param[out] Z
Expand Down Expand Up @@ -454,7 +454,7 @@ SUBROUTINE DLASD7( ICOMPQ, NL, NR, SQRE, K, D, Z, ZW, VF, VFW, VL,
*
* Check if singular values are close enough to allow deflation.
*
IF( ABS( D( J )-D( JPREV ) ).LE.TOL ) THEN
IF( ( D( J )-D( JPREV ) ).LE.TOL ) THEN
*
* Deflation is possible.
*
Expand Down Expand Up @@ -490,7 +490,14 @@ SUBROUTINE DLASD7( ICOMPQ, NL, NR, SQRE, K, D, Z, ZW, VF, VFW, VL,
CALL DROT( 1, VF( JPREV ), 1, VF( J ), 1, C, S )
CALL DROT( 1, VL( JPREV ), 1, VL( J ), 1, C, S )
K2 = K2 - 1
IDXP( K2 ) = JPREV
*
* Insert the deflated index in the correct position in IDXP.
* If J - JPREV is greater than 1, the indices in between
* must be shifted to preserve the correct output order.
*
DO 130 JP = JPREV, J - 1
IDXP( K2 + J - 1 - JP ) = JP
130 CONTINUE
JPREV = J
ELSE
K = K + 1
Expand Down
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