diff options
author | jason <jason@8a072113-8704-0410-8d35-dd094bca7971> | 2008-10-28 01:38:50 +0000 |
---|---|---|
committer | jason <jason@8a072113-8704-0410-8d35-dd094bca7971> | 2008-10-28 01:38:50 +0000 |
commit | baba851215b44ac3b60b9248eb02bcce7eb76247 (patch) | |
tree | 8c0f5c006875532a30d4409f5e94b0f310ff00a7 /SRC/zptts2.f | |
download | lapack-baba851215b44ac3b60b9248eb02bcce7eb76247.tar.gz lapack-baba851215b44ac3b60b9248eb02bcce7eb76247.tar.bz2 lapack-baba851215b44ac3b60b9248eb02bcce7eb76247.zip |
Move LAPACK trunk into position.
Diffstat (limited to 'SRC/zptts2.f')
-rw-r--r-- | SRC/zptts2.f | 176 |
1 files changed, 176 insertions, 0 deletions
diff --git a/SRC/zptts2.f b/SRC/zptts2.f new file mode 100644 index 00000000..e2a90fc3 --- /dev/null +++ b/SRC/zptts2.f @@ -0,0 +1,176 @@ + SUBROUTINE ZPTTS2( IUPLO, N, NRHS, D, E, B, LDB ) +* +* -- LAPACK routine (version 3.1) -- +* Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. +* November 2006 +* +* .. Scalar Arguments .. + INTEGER IUPLO, LDB, N, NRHS +* .. +* .. Array Arguments .. + DOUBLE PRECISION D( * ) + COMPLEX*16 B( LDB, * ), E( * ) +* .. +* +* Purpose +* ======= +* +* ZPTTS2 solves a tridiagonal system of the form +* A * X = B +* using the factorization A = U'*D*U or A = L*D*L' computed by ZPTTRF. +* D is a diagonal matrix specified in the vector D, U (or L) is a unit +* bidiagonal matrix whose superdiagonal (subdiagonal) is specified in +* the vector E, and X and B are N by NRHS matrices. +* +* Arguments +* ========= +* +* IUPLO (input) INTEGER +* Specifies the form of the factorization and whether the +* vector E is the superdiagonal of the upper bidiagonal factor +* U or the subdiagonal of the lower bidiagonal factor L. +* = 1: A = U'*D*U, E is the superdiagonal of U +* = 0: A = L*D*L', E is the subdiagonal of L +* +* N (input) INTEGER +* The order of the tridiagonal matrix A. N >= 0. +* +* NRHS (input) INTEGER +* The number of right hand sides, i.e., the number of columns +* of the matrix B. NRHS >= 0. +* +* D (input) DOUBLE PRECISION array, dimension (N) +* The n diagonal elements of the diagonal matrix D from the +* factorization A = U'*D*U or A = L*D*L'. +* +* E (input) COMPLEX*16 array, dimension (N-1) +* If IUPLO = 1, the (n-1) superdiagonal elements of the unit +* bidiagonal factor U from the factorization A = U'*D*U. +* If IUPLO = 0, the (n-1) subdiagonal elements of the unit +* bidiagonal factor L from the factorization A = L*D*L'. +* +* B (input/output) DOUBLE PRECISION array, dimension (LDB,NRHS) +* On entry, the right hand side vectors B for the system of +* linear equations. +* On exit, the solution vectors, X. +* +* LDB (input) INTEGER +* The leading dimension of the array B. LDB >= max(1,N). +* +* ===================================================================== +* +* .. Local Scalars .. + INTEGER I, J +* .. +* .. External Subroutines .. + EXTERNAL ZDSCAL +* .. +* .. Intrinsic Functions .. + INTRINSIC DCONJG +* .. +* .. Executable Statements .. +* +* Quick return if possible +* + IF( N.LE.1 ) THEN + IF( N.EQ.1 ) + $ CALL ZDSCAL( NRHS, 1.D0 / D( 1 ), B, LDB ) + RETURN + END IF +* + IF( IUPLO.EQ.1 ) THEN +* +* Solve A * X = B using the factorization A = U'*D*U, +* overwriting each right hand side vector with its solution. +* + IF( NRHS.LE.2 ) THEN + J = 1 + 10 CONTINUE +* +* Solve U' * x = b. +* + DO 20 I = 2, N + B( I, J ) = B( I, J ) - B( I-1, J )*DCONJG( E( I-1 ) ) + 20 CONTINUE +* +* Solve D * U * x = b. +* + DO 30 I = 1, N + B( I, J ) = B( I, J ) / D( I ) + 30 CONTINUE + DO 40 I = N - 1, 1, -1 + B( I, J ) = B( I, J ) - B( I+1, J )*E( I ) + 40 CONTINUE + IF( J.LT.NRHS ) THEN + J = J + 1 + GO TO 10 + END IF + ELSE + DO 70 J = 1, NRHS +* +* Solve U' * x = b. +* + DO 50 I = 2, N + B( I, J ) = B( I, J ) - B( I-1, J )*DCONJG( E( I-1 ) ) + 50 CONTINUE +* +* Solve D * U * x = b. +* + B( N, J ) = B( N, J ) / D( N ) + DO 60 I = N - 1, 1, -1 + B( I, J ) = B( I, J ) / D( I ) - B( I+1, J )*E( I ) + 60 CONTINUE + 70 CONTINUE + END IF + ELSE +* +* Solve A * X = B using the factorization A = L*D*L', +* overwriting each right hand side vector with its solution. +* + IF( NRHS.LE.2 ) THEN + J = 1 + 80 CONTINUE +* +* Solve L * x = b. +* + DO 90 I = 2, N + B( I, J ) = B( I, J ) - B( I-1, J )*E( I-1 ) + 90 CONTINUE +* +* Solve D * L' * x = b. +* + DO 100 I = 1, N + B( I, J ) = B( I, J ) / D( I ) + 100 CONTINUE + DO 110 I = N - 1, 1, -1 + B( I, J ) = B( I, J ) - B( I+1, J )*DCONJG( E( I ) ) + 110 CONTINUE + IF( J.LT.NRHS ) THEN + J = J + 1 + GO TO 80 + END IF + ELSE + DO 140 J = 1, NRHS +* +* Solve L * x = b. +* + DO 120 I = 2, N + B( I, J ) = B( I, J ) - B( I-1, J )*E( I-1 ) + 120 CONTINUE +* +* Solve D * L' * x = b. +* + B( N, J ) = B( N, J ) / D( N ) + DO 130 I = N - 1, 1, -1 + B( I, J ) = B( I, J ) / D( I ) - + $ B( I+1, J )*DCONJG( E( I ) ) + 130 CONTINUE + 140 CONTINUE + END IF + END IF +* + RETURN +* +* End of ZPTTS2 +* + END |