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|
/* dsptrf.f -- translated by f2c (version 20060506).
You must link the resulting object file with libf2c:
on Microsoft Windows system, link with libf2c.lib;
on Linux or Unix systems, link with .../path/to/libf2c.a -lm
or, if you install libf2c.a in a standard place, with -lf2c -lm
-- in that order, at the end of the command line, as in
cc *.o -lf2c -lm
Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,
http://www.netlib.org/f2c/libf2c.zip
*/
#ifdef __cplusplus
extern "C" {
#endif
#include "v3p_netlib.h"
/* Table of constant values */
static integer c__1 = 1;
/*< SUBROUTINE DSPTRF( UPLO, N, AP, IPIV, INFO ) >*/
/* Subroutine */ int dsptrf_(char *uplo, integer *n, doublereal *ap, integer *ipiv,
integer *info, ftnlen uplo_len)
{
/* System generated locals */
integer i__1;
doublereal d__1, d__2, d__3;
/* Builtin functions */
double sqrt(doublereal);
/* Local variables */
doublereal c__;
integer j, k;
doublereal s, t, r1, r2;
integer kc, kk, kp, kx, knc, kpc=0, npp, imax=0, jmax;
extern /* Subroutine */ int drot_(integer *, doublereal *, integer *,
doublereal *, integer *, doublereal *, doublereal *), dspr_(char *
, integer *, doublereal *, doublereal *, integer *, doublereal *,
ftnlen);
doublereal alpha;
extern /* Subroutine */ int dscal_(integer *, doublereal *, doublereal *,
integer *);
extern logical lsame_(char *, char *, ftnlen, ftnlen);
extern /* Subroutine */ int dswap_(integer *, doublereal *, integer *,
doublereal *, integer *);
integer kstep;
logical upper;
extern /* Subroutine */ int dlaev2_(doublereal *, doublereal *,
doublereal *, doublereal *, doublereal *, doublereal *,
doublereal *);
doublereal absakk;
extern integer idamax_(integer *, doublereal *, integer *);
extern /* Subroutine */ int xerbla_(char *, integer *, ftnlen);
doublereal colmax, rowmax;
(void)uplo_len;
/* -- LAPACK routine (version 2.0) -- */
/* Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd., */
/* Courant Institute, Argonne National Lab, and Rice University */
/* March 31, 1993 */
/* .. Scalar Arguments .. */
/*< CHARACTER UPLO >*/
/*< INTEGER INFO, N >*/
/* .. */
/* .. Array Arguments .. */
/*< INTEGER IPIV( * ) >*/
/*< DOUBLE PRECISION AP( * ) >*/
/* .. */
/* Purpose */
/* ======= */
/* DSPTRF computes the factorization of a real symmetric matrix A stored */
/* in packed format using the Bunch-Kaufman diagonal pivoting method: */
/* A = U*D*U**T or A = L*D*L**T */
/* where U (or L) is a product of permutation and unit upper (lower) */
/* triangular matrices, and D is symmetric and block diagonal with */
/* 1-by-1 and 2-by-2 diagonal blocks. */
/* Arguments */
/* ========= */
/* UPLO (input) CHARACTER*1 */
/* = 'U': Upper triangle of A is stored; */
/* = 'L': Lower triangle of A is stored. */
/* N (input) INTEGER */
/* The order of the matrix A. N >= 0. */
/* AP (input/output) DOUBLE PRECISION array, dimension (N*(N+1)/2) */
/* On entry, the upper or lower triangle of the symmetric matrix */
/* A, packed columnwise in a linear array. The j-th column of A */
/* is stored in the array AP as follows: */
/* if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1<=i<=j; */
/* if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = A(i,j) for j<=i<=n. */
/* On exit, the block diagonal matrix D and the multipliers used */
/* to obtain the factor U or L, stored as a packed triangular */
/* matrix overwriting A (see below for further details). */
/* IPIV (output) INTEGER array, dimension (N) */
/* Details of the interchanges and the block structure of D. */
/* If IPIV(k) > 0, then rows and columns k and IPIV(k) were */
/* interchanged and D(k,k) is a 1-by-1 diagonal block. */
/* If UPLO = 'U' and IPIV(k) = IPIV(k-1) < 0, then rows and */
/* columns k-1 and -IPIV(k) were interchanged and D(k-1:k,k-1:k) */
/* is a 2-by-2 diagonal block. If UPLO = 'L' and IPIV(k) = */
/* IPIV(k+1) < 0, then rows and columns k+1 and -IPIV(k) were */
/* interchanged and D(k:k+1,k:k+1) is a 2-by-2 diagonal block. */
/* INFO (output) INTEGER */
/* = 0: successful exit */
/* < 0: if INFO = -i, the i-th argument had an illegal value */
/* > 0: if INFO = i, D(i,i) is exactly zero. The factorization */
/* has been completed, but the block diagonal matrix D is */
/* exactly singular, and division by zero will occur if it */
/* is used to solve a system of equations. */
/* Further Details */
/* =============== */
/* If UPLO = 'U', then A = U*D*U', where */
/* U = P(n)*U(n)* ... *P(k)U(k)* ..., */
/* i.e., U is a product of terms P(k)*U(k), where k decreases from n to */
/* 1 in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1 */
/* and 2-by-2 diagonal blocks D(k). P(k) is a permutation matrix as */
/* defined by IPIV(k), and U(k) is a unit upper triangular matrix, such */
/* that if the diagonal block D(k) is of order s (s = 1 or 2), then */
/* ( I v 0 ) k-s */
/* U(k) = ( 0 I 0 ) s */
/* ( 0 0 I ) n-k */
/* k-s s n-k */
/* If s = 1, D(k) overwrites A(k,k), and v overwrites A(1:k-1,k). */
/* If s = 2, the upper triangle of D(k) overwrites A(k-1,k-1), A(k-1,k), */
/* and A(k,k), and v overwrites A(1:k-2,k-1:k). */
/* If UPLO = 'L', then A = L*D*L', where */
/* L = P(1)*L(1)* ... *P(k)*L(k)* ..., */
/* i.e., L is a product of terms P(k)*L(k), where k increases from 1 to */
/* n in steps of 1 or 2, and D is a block diagonal matrix with 1-by-1 */
/* and 2-by-2 diagonal blocks D(k). P(k) is a permutation matrix as */
/* defined by IPIV(k), and L(k) is a unit lower triangular matrix, such */
/* that if the diagonal block D(k) is of order s (s = 1 or 2), then */
/* ( I 0 0 ) k-1 */
/* L(k) = ( 0 I 0 ) s */
/* ( 0 v I ) n-k-s+1 */
/* k-1 s n-k-s+1 */
/* If s = 1, D(k) overwrites A(k,k), and v overwrites A(k+1:n,k). */
/* If s = 2, the lower triangle of D(k) overwrites A(k,k), A(k+1,k), */
/* and A(k+1,k+1), and v overwrites A(k+2:n,k:k+1). */
/* ===================================================================== */
/* .. Parameters .. */
/*< DOUBLE PRECISION ZERO, ONE >*/
/*< PARAMETER ( ZERO = 0.0D+0, ONE = 1.0D+0 ) >*/
/*< DOUBLE PRECISION EIGHT, SEVTEN >*/
/*< PARAMETER ( EIGHT = 8.0D+0, SEVTEN = 17.0D+0 ) >*/
/* .. */
/* .. Local Scalars .. */
/*< LOGICAL UPPER >*/
/*< >*/
/*< DOUBLE PRECISION ABSAKK, ALPHA, C, COLMAX, R1, R2, ROWMAX, S, T >*/
/* .. */
/* .. External Functions .. */
/*< LOGICAL LSAME >*/
/*< INTEGER IDAMAX >*/
/*< EXTERNAL LSAME, IDAMAX >*/
/* .. */
/* .. External Subroutines .. */
/*< EXTERNAL DLAEV2, DROT, DSCAL, DSPR, DSWAP, XERBLA >*/
/* .. */
/* .. Intrinsic Functions .. */
/*< INTRINSIC ABS, MAX, SQRT >*/
/* .. */
/* .. Executable Statements .. */
/* Test the input parameters. */
/*< INFO = 0 >*/
/* Parameter adjustments */
--ipiv;
--ap;
/* Function Body */
*info = 0;
/*< UPPER = LSAME( UPLO, 'U' ) >*/
upper = lsame_(uplo, "U", (ftnlen)1, (ftnlen)1);
/*< IF( .NOT.UPPER .AND. .NOT.LSAME( UPLO, 'L' ) ) THEN >*/
if (! upper && ! lsame_(uplo, "L", (ftnlen)1, (ftnlen)1)) {
/*< INFO = -1 >*/
*info = -1;
/*< ELSE IF( N.LT.0 ) THEN >*/
} else if (*n < 0) {
/*< INFO = -2 >*/
*info = -2;
/*< END IF >*/
}
/*< IF( INFO.NE.0 ) THEN >*/
if (*info != 0) {
/*< CALL XERBLA( 'DSPTRF', -INFO ) >*/
i__1 = -(*info);
xerbla_("DSPTRF", &i__1, (ftnlen)6);
/*< RETURN >*/
return 0;
/*< END IF >*/
}
/* Initialize ALPHA for use in choosing pivot block size. */
/*< ALPHA = ( ONE+SQRT( SEVTEN ) ) / EIGHT >*/
alpha = (sqrt(17.) + 1.) / 8.;
/*< IF( UPPER ) THEN >*/
if (upper) {
/* Factorize A as U*D*U' using the upper triangle of A */
/* K is the main loop index, decreasing from N to 1 in steps of */
/* 1 or 2 */
/*< K = N >*/
k = *n;
/*< KC = ( N-1 )*N / 2 + 1 >*/
kc = (*n - 1) * *n / 2 + 1;
/*< 10 CONTINUE >*/
L10:
/*< KNC = KC >*/
knc = kc;
/* If K < 1, exit from loop */
/*< >*/
if (k < 1) {
goto L70;
}
/*< KSTEP = 1 >*/
kstep = 1;
/* Determine rows and columns to be interchanged and whether */
/* a 1-by-1 or 2-by-2 pivot block will be used */
/*< ABSAKK = ABS( AP( KC+K-1 ) ) >*/
absakk = (d__1 = ap[kc + k - 1], abs(d__1));
/* IMAX is the row-index of the largest off-diagonal element in */
/* column K, and COLMAX is its absolute value */
/*< IF( K.GT.1 ) THEN >*/
if (k > 1) {
/*< IMAX = IDAMAX( K-1, AP( KC ), 1 ) >*/
i__1 = k - 1;
imax = idamax_(&i__1, &ap[kc], &c__1);
/*< COLMAX = ABS( AP( KC+IMAX-1 ) ) >*/
colmax = (d__1 = ap[kc + imax - 1], abs(d__1));
/*< ELSE >*/
} else {
/*< COLMAX = ZERO >*/
colmax = 0.;
/*< END IF >*/
}
/*< IF( MAX( ABSAKK, COLMAX ).EQ.ZERO ) THEN >*/
if (max(absakk,colmax) == 0.) {
/* Column K is zero: set INFO and continue */
/*< >*/
if (*info == 0) {
*info = k;
}
/*< KP = K >*/
kp = k;
/*< ELSE >*/
} else {
/*< IF( ABSAKK.GE.ALPHA*COLMAX ) THEN >*/
if (absakk >= alpha * colmax) {
/* no interchange, use 1-by-1 pivot block */
/*< KP = K >*/
kp = k;
/*< ELSE >*/
} else {
/* JMAX is the column-index of the largest off-diagonal */
/* element in row IMAX, and ROWMAX is its absolute value */
/*< ROWMAX = ZERO >*/
rowmax = 0.;
/*< JMAX = IMAX >*/
jmax = imax;
/*< KX = IMAX*( IMAX+1 ) / 2 + IMAX >*/
kx = imax * (imax + 1) / 2 + imax;
/*< DO 20 J = IMAX + 1, K >*/
i__1 = k;
for (j = imax + 1; j <= i__1; ++j) {
/*< IF( ABS( AP( KX ) ).GT.ROWMAX ) THEN >*/
if ((d__1 = ap[kx], abs(d__1)) > rowmax) {
/*< ROWMAX = ABS( AP( KX ) ) >*/
rowmax = (d__1 = ap[kx], abs(d__1));
/*< JMAX = J >*/
jmax = j;
/*< END IF >*/
}
/*< KX = KX + J >*/
kx += j;
/*< 20 CONTINUE >*/
/* L20: */
}
/*< KPC = ( IMAX-1 )*IMAX / 2 + 1 >*/
kpc = (imax - 1) * imax / 2 + 1;
/*< IF( IMAX.GT.1 ) THEN >*/
if (imax > 1) {
/*< JMAX = IDAMAX( IMAX-1, AP( KPC ), 1 ) >*/
i__1 = imax - 1;
jmax = idamax_(&i__1, &ap[kpc], &c__1);
/*< ROWMAX = MAX( ROWMAX, ABS( AP( KPC+JMAX-1 ) ) ) >*/
/* Computing MAX */
d__2 = rowmax, d__3 = (d__1 = ap[kpc + jmax - 1], abs(
d__1));
rowmax = max(d__2,d__3);
/*< END IF >*/
}
/*< IF( ABSAKK.GE.ALPHA*COLMAX*( COLMAX / ROWMAX ) ) THEN >*/
if (absakk >= alpha * colmax * (colmax / rowmax)) {
/* no interchange, use 1-by-1 pivot block */
/*< KP = K >*/
kp = k;
/*< ELSE IF( ABS( AP( KPC+IMAX-1 ) ).GE.ALPHA*ROWMAX ) THEN >*/
} else if ((d__1 = ap[kpc + imax - 1], abs(d__1)) >= alpha *
rowmax) {
/* interchange rows and columns K and IMAX, use 1-by-1 */
/* pivot block */
/*< KP = IMAX >*/
kp = imax;
/*< ELSE >*/
} else {
/* interchange rows and columns K-1 and IMAX, use 2-by-2 */
/* pivot block */
/*< KP = IMAX >*/
kp = imax;
/*< KSTEP = 2 >*/
kstep = 2;
/*< END IF >*/
}
/*< END IF >*/
}
/*< KK = K - KSTEP + 1 >*/
kk = k - kstep + 1;
/*< >*/
if (kstep == 2) {
knc = knc - k + 1;
}
/*< IF( KP.NE.KK ) THEN >*/
if (kp != kk) {
/* Interchange rows and columns KK and KP in the leading */
/* submatrix A(1:k,1:k) */
/*< CALL DSWAP( KP-1, AP( KNC ), 1, AP( KPC ), 1 ) >*/
i__1 = kp - 1;
dswap_(&i__1, &ap[knc], &c__1, &ap[kpc], &c__1);
/*< KX = KPC + KP - 1 >*/
kx = kpc + kp - 1;
/*< DO 30 J = KP + 1, KK - 1 >*/
i__1 = kk - 1;
for (j = kp + 1; j <= i__1; ++j) {
/*< KX = KX + J - 1 >*/
kx = kx + j - 1;
/*< T = AP( KNC+J-1 ) >*/
t = ap[knc + j - 1];
/*< AP( KNC+J-1 ) = AP( KX ) >*/
ap[knc + j - 1] = ap[kx];
/*< AP( KX ) = T >*/
ap[kx] = t;
/*< 30 CONTINUE >*/
/* L30: */
}
/*< T = AP( KNC+KK-1 ) >*/
t = ap[knc + kk - 1];
/*< AP( KNC+KK-1 ) = AP( KPC+KP-1 ) >*/
ap[knc + kk - 1] = ap[kpc + kp - 1];
/*< AP( KPC+KP-1 ) = T >*/
ap[kpc + kp - 1] = t;
/*< IF( KSTEP.EQ.2 ) THEN >*/
if (kstep == 2) {
/*< T = AP( KC+K-2 ) >*/
t = ap[kc + k - 2];
/*< AP( KC+K-2 ) = AP( KC+KP-1 ) >*/
ap[kc + k - 2] = ap[kc + kp - 1];
/*< AP( KC+KP-1 ) = T >*/
ap[kc + kp - 1] = t;
/*< END IF >*/
}
/*< END IF >*/
}
/* Update the leading submatrix */
/*< IF( KSTEP.EQ.1 ) THEN >*/
if (kstep == 1) {
/* 1-by-1 pivot block D(k): column k now holds */
/* W(k) = U(k)*D(k) */
/* where U(k) is the k-th column of U */
/* Perform a rank-1 update of A(1:k-1,1:k-1) as */
/* A := A - U(k)*D(k)*U(k)' = A - W(k)*1/D(k)*W(k)' */
/*< R1 = ONE / AP( KC+K-1 ) >*/
r1 = 1. / ap[kc + k - 1];
/*< CALL DSPR( UPLO, K-1, -R1, AP( KC ), 1, AP ) >*/
i__1 = k - 1;
d__1 = -r1;
dspr_(uplo, &i__1, &d__1, &ap[kc], &c__1, &ap[1], (ftnlen)1);
/* Store U(k) in column k */
/*< CALL DSCAL( K-1, R1, AP( KC ), 1 ) >*/
i__1 = k - 1;
dscal_(&i__1, &r1, &ap[kc], &c__1);
/*< ELSE >*/
} else {
/* 2-by-2 pivot block D(k): columns k and k-1 now hold */
/* ( W(k-1) W(k) ) = ( U(k-1) U(k) )*D(k) */
/* where U(k) and U(k-1) are the k-th and (k-1)-th columns */
/* of U */
/* Perform a rank-2 update of A(1:k-2,1:k-2) as */
/* A := A - ( U(k-1) U(k) )*D(k)*( U(k-1) U(k) )' */
/* = A - ( W(k-1) W(k) )*inv(D(k))*( W(k-1) W(k) )' */
/* Convert this to two rank-1 updates by using the eigen- */
/* decomposition of D(k) */
/*< >*/
dlaev2_(&ap[kc - 1], &ap[kc + k - 2], &ap[kc + k - 1], &r1, &
r2, &c__, &s);
/*< R1 = ONE / R1 >*/
r1 = 1. / r1;
/*< R2 = ONE / R2 >*/
r2 = 1. / r2;
/*< CALL DROT( K-2, AP( KNC ), 1, AP( KC ), 1, C, S ) >*/
i__1 = k - 2;
drot_(&i__1, &ap[knc], &c__1, &ap[kc], &c__1, &c__, &s);
/*< CALL DSPR( UPLO, K-2, -R1, AP( KNC ), 1, AP ) >*/
i__1 = k - 2;
d__1 = -r1;
dspr_(uplo, &i__1, &d__1, &ap[knc], &c__1, &ap[1], (ftnlen)1);
/*< CALL DSPR( UPLO, K-2, -R2, AP( KC ), 1, AP ) >*/
i__1 = k - 2;
d__1 = -r2;
dspr_(uplo, &i__1, &d__1, &ap[kc], &c__1, &ap[1], (ftnlen)1);
/* Store U(k) and U(k-1) in columns k and k-1 */
/*< CALL DSCAL( K-2, R1, AP( KNC ), 1 ) >*/
i__1 = k - 2;
dscal_(&i__1, &r1, &ap[knc], &c__1);
/*< CALL DSCAL( K-2, R2, AP( KC ), 1 ) >*/
i__1 = k - 2;
dscal_(&i__1, &r2, &ap[kc], &c__1);
/*< CALL DROT( K-2, AP( KNC ), 1, AP( KC ), 1, C, -S ) >*/
i__1 = k - 2;
d__1 = -s;
drot_(&i__1, &ap[knc], &c__1, &ap[kc], &c__1, &c__, &d__1);
/*< END IF >*/
}
/*< END IF >*/
}
/* Store details of the interchanges in IPIV */
/*< IF( KSTEP.EQ.1 ) THEN >*/
if (kstep == 1) {
/*< IPIV( K ) = KP >*/
ipiv[k] = kp;
/*< ELSE >*/
} else {
/*< IPIV( K ) = -KP >*/
ipiv[k] = -kp;
/*< IPIV( K-1 ) = -KP >*/
ipiv[k - 1] = -kp;
/*< END IF >*/
}
/* Decrease K and return to the start of the main loop */
/*< K = K - KSTEP >*/
k -= kstep;
/*< KC = KNC - K >*/
kc = knc - k;
/*< GO TO 10 >*/
goto L10;
/*< ELSE >*/
} else {
/* Factorize A as L*D*L' using the lower triangle of A */
/* K is the main loop index, increasing from 1 to N in steps of */
/* 1 or 2 */
/*< K = 1 >*/
k = 1;
/*< KC = 1 >*/
kc = 1;
/*< NPP = N*( N+1 ) / 2 >*/
npp = *n * (*n + 1) / 2;
/*< 40 CONTINUE >*/
L40:
/*< KNC = KC >*/
knc = kc;
/* If K > N, exit from loop */
/*< >*/
if (k > *n) {
goto L70;
}
/*< KSTEP = 1 >*/
kstep = 1;
/* Determine rows and columns to be interchanged and whether */
/* a 1-by-1 or 2-by-2 pivot block will be used */
/*< ABSAKK = ABS( AP( KC ) ) >*/
absakk = (d__1 = ap[kc], abs(d__1));
/* IMAX is the row-index of the largest off-diagonal element in */
/* column K, and COLMAX is its absolute value */
/*< IF( K.LT.N ) THEN >*/
if (k < *n) {
/*< IMAX = K + IDAMAX( N-K, AP( KC+1 ), 1 ) >*/
i__1 = *n - k;
imax = k + idamax_(&i__1, &ap[kc + 1], &c__1);
/*< COLMAX = ABS( AP( KC+IMAX-K ) ) >*/
colmax = (d__1 = ap[kc + imax - k], abs(d__1));
/*< ELSE >*/
} else {
/*< COLMAX = ZERO >*/
colmax = 0.;
/*< END IF >*/
}
/*< IF( MAX( ABSAKK, COLMAX ).EQ.ZERO ) THEN >*/
if (max(absakk,colmax) == 0.) {
/* Column K is zero: set INFO and continue */
/*< >*/
if (*info == 0) {
*info = k;
}
/*< KP = K >*/
kp = k;
/*< ELSE >*/
} else {
/*< IF( ABSAKK.GE.ALPHA*COLMAX ) THEN >*/
if (absakk >= alpha * colmax) {
/* no interchange, use 1-by-1 pivot block */
/*< KP = K >*/
kp = k;
/*< ELSE >*/
} else {
/* JMAX is the column-index of the largest off-diagonal */
/* element in row IMAX, and ROWMAX is its absolute value */
/*< ROWMAX = ZERO >*/
rowmax = 0.;
/*< KX = KC + IMAX - K >*/
kx = kc + imax - k;
/*< DO 50 J = K, IMAX - 1 >*/
i__1 = imax - 1;
for (j = k; j <= i__1; ++j) {
/*< IF( ABS( AP( KX ) ).GT.ROWMAX ) THEN >*/
if ((d__1 = ap[kx], abs(d__1)) > rowmax) {
/*< ROWMAX = ABS( AP( KX ) ) >*/
rowmax = (d__1 = ap[kx], abs(d__1));
/*< JMAX = J >*/
jmax = j;
/*< END IF >*/
}
/*< KX = KX + N - J >*/
kx = kx + *n - j;
/*< 50 CONTINUE >*/
/* L50: */
}
/*< KPC = NPP - ( N-IMAX+1 )*( N-IMAX+2 ) / 2 + 1 >*/
kpc = npp - (*n - imax + 1) * (*n - imax + 2) / 2 + 1;
/*< IF( IMAX.LT.N ) THEN >*/
if (imax < *n) {
/*< JMAX = IMAX + IDAMAX( N-IMAX, AP( KPC+1 ), 1 ) >*/
i__1 = *n - imax;
jmax = imax + idamax_(&i__1, &ap[kpc + 1], &c__1);
/*< ROWMAX = MAX( ROWMAX, ABS( AP( KPC+JMAX-IMAX ) ) ) >*/
/* Computing MAX */
d__2 = rowmax, d__3 = (d__1 = ap[kpc + jmax - imax], abs(
d__1));
rowmax = max(d__2,d__3);
/*< END IF >*/
}
/*< IF( ABSAKK.GE.ALPHA*COLMAX*( COLMAX / ROWMAX ) ) THEN >*/
if (absakk >= alpha * colmax * (colmax / rowmax)) {
/* no interchange, use 1-by-1 pivot block */
/*< KP = K >*/
kp = k;
/*< ELSE IF( ABS( AP( KPC ) ).GE.ALPHA*ROWMAX ) THEN >*/
} else if ((d__1 = ap[kpc], abs(d__1)) >= alpha * rowmax) {
/* interchange rows and columns K and IMAX, use 1-by-1 */
/* pivot block */
/*< KP = IMAX >*/
kp = imax;
/*< ELSE >*/
} else {
/* interchange rows and columns K+1 and IMAX, use 2-by-2 */
/* pivot block */
/*< KP = IMAX >*/
kp = imax;
/*< KSTEP = 2 >*/
kstep = 2;
/*< END IF >*/
}
/*< END IF >*/
}
/*< KK = K + KSTEP - 1 >*/
kk = k + kstep - 1;
/*< >*/
if (kstep == 2) {
knc = knc + *n - k + 1;
}
/*< IF( KP.NE.KK ) THEN >*/
if (kp != kk) {
/* Interchange rows and columns KK and KP in the trailing */
/* submatrix A(k:n,k:n) */
/*< >*/
if (kp < *n) {
i__1 = *n - kp;
dswap_(&i__1, &ap[knc + kp - kk + 1], &c__1, &ap[kpc + 1],
&c__1);
}
/*< KX = KNC + KP - KK >*/
kx = knc + kp - kk;
/*< DO 60 J = KK + 1, KP - 1 >*/
i__1 = kp - 1;
for (j = kk + 1; j <= i__1; ++j) {
/*< KX = KX + N - J + 1 >*/
kx = kx + *n - j + 1;
/*< T = AP( KNC+J-KK ) >*/
t = ap[knc + j - kk];
/*< AP( KNC+J-KK ) = AP( KX ) >*/
ap[knc + j - kk] = ap[kx];
/*< AP( KX ) = T >*/
ap[kx] = t;
/*< 60 CONTINUE >*/
/* L60: */
}
/*< T = AP( KNC ) >*/
t = ap[knc];
/*< AP( KNC ) = AP( KPC ) >*/
ap[knc] = ap[kpc];
/*< AP( KPC ) = T >*/
ap[kpc] = t;
/*< IF( KSTEP.EQ.2 ) THEN >*/
if (kstep == 2) {
/*< T = AP( KC+1 ) >*/
t = ap[kc + 1];
/*< AP( KC+1 ) = AP( KC+KP-K ) >*/
ap[kc + 1] = ap[kc + kp - k];
/*< AP( KC+KP-K ) = T >*/
ap[kc + kp - k] = t;
/*< END IF >*/
}
/*< END IF >*/
}
/* Update the trailing submatrix */
/*< IF( KSTEP.EQ.1 ) THEN >*/
if (kstep == 1) {
/* 1-by-1 pivot block D(k): column k now holds */
/* W(k) = L(k)*D(k) */
/* where L(k) is the k-th column of L */
/*< IF( K.LT.N ) THEN >*/
if (k < *n) {
/* Perform a rank-1 update of A(k+1:n,k+1:n) as */
/* A := A - L(k)*D(k)*L(k)' = A - W(k)*(1/D(k))*W(k)' */
/*< R1 = ONE / AP( KC ) >*/
r1 = 1. / ap[kc];
/*< >*/
i__1 = *n - k;
d__1 = -r1;
dspr_(uplo, &i__1, &d__1, &ap[kc + 1], &c__1, &ap[kc + *n
- k + 1], (ftnlen)1);
/* Store L(k) in column K */
/*< CALL DSCAL( N-K, R1, AP( KC+1 ), 1 ) >*/
i__1 = *n - k;
dscal_(&i__1, &r1, &ap[kc + 1], &c__1);
/*< END IF >*/
}
/*< ELSE >*/
} else {
/* 2-by-2 pivot block D(k): columns K and K+1 now hold */
/* ( W(k) W(k+1) ) = ( L(k) L(k+1) )*D(k) */
/* where L(k) and L(k+1) are the k-th and (k+1)-th columns */
/* of L */
/*< IF( K.LT.N-1 ) THEN >*/
if (k < *n - 1) {
/* Perform a rank-2 update of A(k+2:n,k+2:n) as */
/* A := A - ( L(k) L(k+1) )*D(k)*( L(k) L(k+1) )' */
/* = A - ( W(k) W(k+1) )*inv(D(k))*( W(k) W(k+1) )' */
/* Convert this to two rank-1 updates by using the eigen- */
/* decomposition of D(k) */
/*< >*/
dlaev2_(&ap[kc], &ap[kc + 1], &ap[knc], &r1, &r2, &c__, &
s);
/*< R1 = ONE / R1 >*/
r1 = 1. / r1;
/*< R2 = ONE / R2 >*/
r2 = 1. / r2;
/*< >*/
i__1 = *n - k - 1;
drot_(&i__1, &ap[kc + 2], &c__1, &ap[knc + 1], &c__1, &
c__, &s);
/*< >*/
i__1 = *n - k - 1;
d__1 = -r1;
dspr_(uplo, &i__1, &d__1, &ap[kc + 2], &c__1, &ap[knc + *
n - k], (ftnlen)1);
/*< >*/
i__1 = *n - k - 1;
d__1 = -r2;
dspr_(uplo, &i__1, &d__1, &ap[knc + 1], &c__1, &ap[knc + *
n - k], (ftnlen)1);
/* Store L(k) and L(k+1) in columns k and k+1 */
/*< CALL DSCAL( N-K-1, R1, AP( KC+2 ), 1 ) >*/
i__1 = *n - k - 1;
dscal_(&i__1, &r1, &ap[kc + 2], &c__1);
/*< CALL DSCAL( N-K-1, R2, AP( KNC+1 ), 1 ) >*/
i__1 = *n - k - 1;
dscal_(&i__1, &r2, &ap[knc + 1], &c__1);
/*< >*/
i__1 = *n - k - 1;
d__1 = -s;
drot_(&i__1, &ap[kc + 2], &c__1, &ap[knc + 1], &c__1, &
c__, &d__1);
/*< END IF >*/
}
/*< END IF >*/
}
/*< END IF >*/
}
/* Store details of the interchanges in IPIV */
/*< IF( KSTEP.EQ.1 ) THEN >*/
if (kstep == 1) {
/*< IPIV( K ) = KP >*/
ipiv[k] = kp;
/*< ELSE >*/
} else {
/*< IPIV( K ) = -KP >*/
ipiv[k] = -kp;
/*< IPIV( K+1 ) = -KP >*/
ipiv[k + 1] = -kp;
/*< END IF >*/
}
/* Increase K and return to the start of the main loop */
/*< K = K + KSTEP >*/
k += kstep;
/*< KC = KNC + N - K + 2 >*/
kc = knc + *n - k + 2;
/*< GO TO 40 >*/
goto L40;
/*< END IF >*/
}
/*< 70 CONTINUE >*/
L70:
/*< RETURN >*/
return 0;
/* End of DSPTRF */
/*< END >*/
} /* dsptrf_ */
#ifdef __cplusplus
}
#endif
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