1*> \brief \b SSYSVXX 2* 3* =========== DOCUMENTATION =========== 4* 5* Online html documentation available at 6* http://www.netlib.org/lapack/explore-html/ 7* 8*> \htmlonly 9*> Download SSYSVXX + dependencies 10*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/ssysvxx.f"> 11*> [TGZ]</a> 12*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/ssysvxx.f"> 13*> [ZIP]</a> 14*> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/ssysvxx.f"> 15*> [TXT]</a> 16*> \endhtmlonly 17* 18* Definition: 19* =========== 20* 21* SUBROUTINE SSYSVXX( FACT, UPLO, N, NRHS, A, LDA, AF, LDAF, IPIV, 22* EQUED, S, B, LDB, X, LDX, RCOND, RPVGRW, BERR, 23* N_ERR_BNDS, ERR_BNDS_NORM, ERR_BNDS_COMP, 24* NPARAMS, PARAMS, WORK, IWORK, INFO ) 25* 26* .. Scalar Arguments .. 27* CHARACTER EQUED, FACT, UPLO 28* INTEGER INFO, LDA, LDAF, LDB, LDX, N, NRHS, NPARAMS, 29* $ N_ERR_BNDS 30* REAL RCOND, RPVGRW 31* .. 32* .. Array Arguments .. 33* INTEGER IPIV( * ), IWORK( * ) 34* REAL A( LDA, * ), AF( LDAF, * ), B( LDB, * ), 35* $ X( LDX, * ), WORK( * ) 36* REAL S( * ), PARAMS( * ), BERR( * ), 37* $ ERR_BNDS_NORM( NRHS, * ), 38* $ ERR_BNDS_COMP( NRHS, * ) 39* .. 40* 41* 42*> \par Purpose: 43* ============= 44*> 45*> \verbatim 46*> 47*> SSYSVXX uses the diagonal pivoting factorization to compute the 48*> solution to a real system of linear equations A * X = B, where A 49*> is an N-by-N symmetric matrix and X and B are N-by-NRHS matrices. 50*> 51*> If requested, both normwise and maximum componentwise error bounds 52*> are returned. SSYSVXX will return a solution with a tiny 53*> guaranteed error (O(eps) where eps is the working machine 54*> precision) unless the matrix is very ill-conditioned, in which 55*> case a warning is returned. Relevant condition numbers also are 56*> calculated and returned. 57*> 58*> SSYSVXX accepts user-provided factorizations and equilibration 59*> factors; see the definitions of the FACT and EQUED options. 60*> Solving with refinement and using a factorization from a previous 61*> SSYSVXX call will also produce a solution with either O(eps) 62*> errors or warnings, but we cannot make that claim for general 63*> user-provided factorizations and equilibration factors if they 64*> differ from what SSYSVXX would itself produce. 65*> \endverbatim 66* 67*> \par Description: 68* ================= 69*> 70*> \verbatim 71*> 72*> The following steps are performed: 73*> 74*> 1. If FACT = 'E', real scaling factors are computed to equilibrate 75*> the system: 76*> 77*> diag(S)*A*diag(S) *inv(diag(S))*X = diag(S)*B 78*> 79*> Whether or not the system will be equilibrated depends on the 80*> scaling of the matrix A, but if equilibration is used, A is 81*> overwritten by diag(S)*A*diag(S) and B by diag(S)*B. 82*> 83*> 2. If FACT = 'N' or 'E', the LU decomposition is used to factor 84*> the matrix A (after equilibration if FACT = 'E') as 85*> 86*> A = U * D * U**T, if UPLO = 'U', or 87*> A = L * D * L**T, if UPLO = 'L', 88*> 89*> where U (or L) is a product of permutation and unit upper (lower) 90*> triangular matrices, and D is symmetric and block diagonal with 91*> 1-by-1 and 2-by-2 diagonal blocks. 92*> 93*> 3. If some D(i,i)=0, so that D is exactly singular, then the 94*> routine returns with INFO = i. Otherwise, the factored form of A 95*> is used to estimate the condition number of the matrix A (see 96*> argument RCOND). If the reciprocal of the condition number is 97*> less than machine precision, the routine still goes on to solve 98*> for X and compute error bounds as described below. 99*> 100*> 4. The system of equations is solved for X using the factored form 101*> of A. 102*> 103*> 5. By default (unless PARAMS(LA_LINRX_ITREF_I) is set to zero), 104*> the routine will use iterative refinement to try to get a small 105*> error and error bounds. Refinement calculates the residual to at 106*> least twice the working precision. 107*> 108*> 6. If equilibration was used, the matrix X is premultiplied by 109*> diag(R) so that it solves the original system before 110*> equilibration. 111*> \endverbatim 112* 113* Arguments: 114* ========== 115* 116*> \verbatim 117*> Some optional parameters are bundled in the PARAMS array. These 118*> settings determine how refinement is performed, but often the 119*> defaults are acceptable. If the defaults are acceptable, users 120*> can pass NPARAMS = 0 which prevents the source code from accessing 121*> the PARAMS argument. 122*> \endverbatim 123*> 124*> \param[in] FACT 125*> \verbatim 126*> FACT is CHARACTER*1 127*> Specifies whether or not the factored form of the matrix A is 128*> supplied on entry, and if not, whether the matrix A should be 129*> equilibrated before it is factored. 130*> = 'F': On entry, AF and IPIV contain the factored form of A. 131*> If EQUED is not 'N', the matrix A has been 132*> equilibrated with scaling factors given by S. 133*> A, AF, and IPIV are not modified. 134*> = 'N': The matrix A will be copied to AF and factored. 135*> = 'E': The matrix A will be equilibrated if necessary, then 136*> copied to AF and factored. 137*> \endverbatim 138*> 139*> \param[in] UPLO 140*> \verbatim 141*> UPLO is CHARACTER*1 142*> = 'U': Upper triangle of A is stored; 143*> = 'L': Lower triangle of A is stored. 144*> \endverbatim 145*> 146*> \param[in] N 147*> \verbatim 148*> N is INTEGER 149*> The number of linear equations, i.e., the order of the 150*> matrix A. N >= 0. 151*> \endverbatim 152*> 153*> \param[in] NRHS 154*> \verbatim 155*> NRHS is INTEGER 156*> The number of right hand sides, i.e., the number of columns 157*> of the matrices B and X. NRHS >= 0. 158*> \endverbatim 159*> 160*> \param[in,out] A 161*> \verbatim 162*> A is REAL array, dimension (LDA,N) 163*> The symmetric matrix A. If UPLO = 'U', the leading N-by-N 164*> upper triangular part of A contains the upper triangular 165*> part of the matrix A, and the strictly lower triangular 166*> part of A is not referenced. If UPLO = 'L', the leading 167*> N-by-N lower triangular part of A contains the lower 168*> triangular part of the matrix A, and the strictly upper 169*> triangular part of A is not referenced. 170*> 171*> On exit, if FACT = 'E' and EQUED = 'Y', A is overwritten by 172*> diag(S)*A*diag(S). 173*> \endverbatim 174*> 175*> \param[in] LDA 176*> \verbatim 177*> LDA is INTEGER 178*> The leading dimension of the array A. LDA >= max(1,N). 179*> \endverbatim 180*> 181*> \param[in,out] AF 182*> \verbatim 183*> AF is REAL array, dimension (LDAF,N) 184*> If FACT = 'F', then AF is an input argument and on entry 185*> contains the block diagonal matrix D and the multipliers 186*> used to obtain the factor U or L from the factorization A = 187*> U*D*U**T or A = L*D*L**T as computed by SSYTRF. 188*> 189*> If FACT = 'N', then AF is an output argument and on exit 190*> returns the block diagonal matrix D and the multipliers 191*> used to obtain the factor U or L from the factorization A = 192*> U*D*U**T or A = L*D*L**T. 193*> \endverbatim 194*> 195*> \param[in] LDAF 196*> \verbatim 197*> LDAF is INTEGER 198*> The leading dimension of the array AF. LDAF >= max(1,N). 199*> \endverbatim 200*> 201*> \param[in,out] IPIV 202*> \verbatim 203*> IPIV is INTEGER array, dimension (N) 204*> If FACT = 'F', then IPIV is an input argument and on entry 205*> contains details of the interchanges and the block 206*> structure of D, as determined by SSYTRF. If IPIV(k) > 0, 207*> then rows and columns k and IPIV(k) were interchanged and 208*> D(k,k) is a 1-by-1 diagonal block. If UPLO = 'U' and 209*> IPIV(k) = IPIV(k-1) < 0, then rows and columns k-1 and 210*> -IPIV(k) were interchanged and D(k-1:k,k-1:k) is a 2-by-2 211*> diagonal block. If UPLO = 'L' and IPIV(k) = IPIV(k+1) < 0, 212*> then rows and columns k+1 and -IPIV(k) were interchanged 213*> and D(k:k+1,k:k+1) is a 2-by-2 diagonal block. 214*> 215*> If FACT = 'N', then IPIV is an output argument and on exit 216*> contains details of the interchanges and the block 217*> structure of D, as determined by SSYTRF. 218*> \endverbatim 219*> 220*> \param[in,out] EQUED 221*> \verbatim 222*> EQUED is CHARACTER*1 223*> Specifies the form of equilibration that was done. 224*> = 'N': No equilibration (always true if FACT = 'N'). 225*> = 'Y': Both row and column equilibration, i.e., A has been 226*> replaced by diag(S) * A * diag(S). 227*> EQUED is an input argument if FACT = 'F'; otherwise, it is an 228*> output argument. 229*> \endverbatim 230*> 231*> \param[in,out] S 232*> \verbatim 233*> S is REAL array, dimension (N) 234*> The scale factors for A. If EQUED = 'Y', A is multiplied on 235*> the left and right by diag(S). S is an input argument if FACT = 236*> 'F'; otherwise, S is an output argument. If FACT = 'F' and EQUED 237*> = 'Y', each element of S must be positive. If S is output, each 238*> element of S is a power of the radix. If S is input, each element 239*> of S should be a power of the radix to ensure a reliable solution 240*> and error estimates. Scaling by powers of the radix does not cause 241*> rounding errors unless the result underflows or overflows. 242*> Rounding errors during scaling lead to refining with a matrix that 243*> is not equivalent to the input matrix, producing error estimates 244*> that may not be reliable. 245*> \endverbatim 246*> 247*> \param[in,out] B 248*> \verbatim 249*> B is REAL array, dimension (LDB,NRHS) 250*> On entry, the N-by-NRHS right hand side matrix B. 251*> On exit, 252*> if EQUED = 'N', B is not modified; 253*> if EQUED = 'Y', B is overwritten by diag(S)*B; 254*> \endverbatim 255*> 256*> \param[in] LDB 257*> \verbatim 258*> LDB is INTEGER 259*> The leading dimension of the array B. LDB >= max(1,N). 260*> \endverbatim 261*> 262*> \param[out] X 263*> \verbatim 264*> X is REAL array, dimension (LDX,NRHS) 265*> If INFO = 0, the N-by-NRHS solution matrix X to the original 266*> system of equations. Note that A and B are modified on exit if 267*> EQUED .ne. 'N', and the solution to the equilibrated system is 268*> inv(diag(S))*X. 269*> \endverbatim 270*> 271*> \param[in] LDX 272*> \verbatim 273*> LDX is INTEGER 274*> The leading dimension of the array X. LDX >= max(1,N). 275*> \endverbatim 276*> 277*> \param[out] RCOND 278*> \verbatim 279*> RCOND is REAL 280*> Reciprocal scaled condition number. This is an estimate of the 281*> reciprocal Skeel condition number of the matrix A after 282*> equilibration (if done). If this is less than the machine 283*> precision (in particular, if it is zero), the matrix is singular 284*> to working precision. Note that the error may still be small even 285*> if this number is very small and the matrix appears ill- 286*> conditioned. 287*> \endverbatim 288*> 289*> \param[out] RPVGRW 290*> \verbatim 291*> RPVGRW is REAL 292*> Reciprocal pivot growth. On exit, this contains the reciprocal 293*> pivot growth factor norm(A)/norm(U). The "max absolute element" 294*> norm is used. If this is much less than 1, then the stability of 295*> the LU factorization of the (equilibrated) matrix A could be poor. 296*> This also means that the solution X, estimated condition numbers, 297*> and error bounds could be unreliable. If factorization fails with 298*> 0<INFO<=N, then this contains the reciprocal pivot growth factor 299*> for the leading INFO columns of A. 300*> \endverbatim 301*> 302*> \param[out] BERR 303*> \verbatim 304*> BERR is REAL array, dimension (NRHS) 305*> Componentwise relative backward error. This is the 306*> componentwise relative backward error of each solution vector X(j) 307*> (i.e., the smallest relative change in any element of A or B that 308*> makes X(j) an exact solution). 309*> \endverbatim 310*> 311*> \param[in] N_ERR_BNDS 312*> \verbatim 313*> N_ERR_BNDS is INTEGER 314*> Number of error bounds to return for each right hand side 315*> and each type (normwise or componentwise). See ERR_BNDS_NORM and 316*> ERR_BNDS_COMP below. 317*> \endverbatim 318*> 319*> \param[out] ERR_BNDS_NORM 320*> \verbatim 321*> ERR_BNDS_NORM is REAL array, dimension (NRHS, N_ERR_BNDS) 322*> For each right-hand side, this array contains information about 323*> various error bounds and condition numbers corresponding to the 324*> normwise relative error, which is defined as follows: 325*> 326*> Normwise relative error in the ith solution vector: 327*> max_j (abs(XTRUE(j,i) - X(j,i))) 328*> ------------------------------ 329*> max_j abs(X(j,i)) 330*> 331*> The array is indexed by the type of error information as described 332*> below. There currently are up to three pieces of information 333*> returned. 334*> 335*> The first index in ERR_BNDS_NORM(i,:) corresponds to the ith 336*> right-hand side. 337*> 338*> The second index in ERR_BNDS_NORM(:,err) contains the following 339*> three fields: 340*> err = 1 "Trust/don't trust" boolean. Trust the answer if the 341*> reciprocal condition number is less than the threshold 342*> sqrt(n) * slamch('Epsilon'). 343*> 344*> err = 2 "Guaranteed" error bound: The estimated forward error, 345*> almost certainly within a factor of 10 of the true error 346*> so long as the next entry is greater than the threshold 347*> sqrt(n) * slamch('Epsilon'). This error bound should only 348*> be trusted if the previous boolean is true. 349*> 350*> err = 3 Reciprocal condition number: Estimated normwise 351*> reciprocal condition number. Compared with the threshold 352*> sqrt(n) * slamch('Epsilon') to determine if the error 353*> estimate is "guaranteed". These reciprocal condition 354*> numbers are 1 / (norm(Z^{-1},inf) * norm(Z,inf)) for some 355*> appropriately scaled matrix Z. 356*> Let Z = S*A, where S scales each row by a power of the 357*> radix so all absolute row sums of Z are approximately 1. 358*> 359*> See Lapack Working Note 165 for further details and extra 360*> cautions. 361*> \endverbatim 362*> 363*> \param[out] ERR_BNDS_COMP 364*> \verbatim 365*> ERR_BNDS_COMP is REAL array, dimension (NRHS, N_ERR_BNDS) 366*> For each right-hand side, this array contains information about 367*> various error bounds and condition numbers corresponding to the 368*> componentwise relative error, which is defined as follows: 369*> 370*> Componentwise relative error in the ith solution vector: 371*> abs(XTRUE(j,i) - X(j,i)) 372*> max_j ---------------------- 373*> abs(X(j,i)) 374*> 375*> The array is indexed by the right-hand side i (on which the 376*> componentwise relative error depends), and the type of error 377*> information as described below. There currently are up to three 378*> pieces of information returned for each right-hand side. If 379*> componentwise accuracy is not requested (PARAMS(3) = 0.0), then 380*> ERR_BNDS_COMP is not accessed. If N_ERR_BNDS < 3, then at most 381*> the first (:,N_ERR_BNDS) entries are returned. 382*> 383*> The first index in ERR_BNDS_COMP(i,:) corresponds to the ith 384*> right-hand side. 385*> 386*> The second index in ERR_BNDS_COMP(:,err) contains the following 387*> three fields: 388*> err = 1 "Trust/don't trust" boolean. Trust the answer if the 389*> reciprocal condition number is less than the threshold 390*> sqrt(n) * slamch('Epsilon'). 391*> 392*> err = 2 "Guaranteed" error bound: The estimated forward error, 393*> almost certainly within a factor of 10 of the true error 394*> so long as the next entry is greater than the threshold 395*> sqrt(n) * slamch('Epsilon'). This error bound should only 396*> be trusted if the previous boolean is true. 397*> 398*> err = 3 Reciprocal condition number: Estimated componentwise 399*> reciprocal condition number. Compared with the threshold 400*> sqrt(n) * slamch('Epsilon') to determine if the error 401*> estimate is "guaranteed". These reciprocal condition 402*> numbers are 1 / (norm(Z^{-1},inf) * norm(Z,inf)) for some 403*> appropriately scaled matrix Z. 404*> Let Z = S*(A*diag(x)), where x is the solution for the 405*> current right-hand side and S scales each row of 406*> A*diag(x) by a power of the radix so all absolute row 407*> sums of Z are approximately 1. 408*> 409*> See Lapack Working Note 165 for further details and extra 410*> cautions. 411*> \endverbatim 412*> 413*> \param[in] NPARAMS 414*> \verbatim 415*> NPARAMS is INTEGER 416*> Specifies the number of parameters set in PARAMS. If <= 0, the 417*> PARAMS array is never referenced and default values are used. 418*> \endverbatim 419*> 420*> \param[in,out] PARAMS 421*> \verbatim 422*> PARAMS is REAL array, dimension NPARAMS 423*> Specifies algorithm parameters. If an entry is < 0.0, then 424*> that entry will be filled with default value used for that 425*> parameter. Only positions up to NPARAMS are accessed; defaults 426*> are used for higher-numbered parameters. 427*> 428*> PARAMS(LA_LINRX_ITREF_I = 1) : Whether to perform iterative 429*> refinement or not. 430*> Default: 1.0 431*> = 0.0: No refinement is performed, and no error bounds are 432*> computed. 433*> = 1.0: Use the double-precision refinement algorithm, 434*> possibly with doubled-single computations if the 435*> compilation environment does not support DOUBLE 436*> PRECISION. 437*> (other values are reserved for future use) 438*> 439*> PARAMS(LA_LINRX_ITHRESH_I = 2) : Maximum number of residual 440*> computations allowed for refinement. 441*> Default: 10 442*> Aggressive: Set to 100 to permit convergence using approximate 443*> factorizations or factorizations other than LU. If 444*> the factorization uses a technique other than 445*> Gaussian elimination, the guarantees in 446*> err_bnds_norm and err_bnds_comp may no longer be 447*> trustworthy. 448*> 449*> PARAMS(LA_LINRX_CWISE_I = 3) : Flag determining if the code 450*> will attempt to find a solution with small componentwise 451*> relative error in the double-precision algorithm. Positive 452*> is true, 0.0 is false. 453*> Default: 1.0 (attempt componentwise convergence) 454*> \endverbatim 455*> 456*> \param[out] WORK 457*> \verbatim 458*> WORK is REAL array, dimension (4*N) 459*> \endverbatim 460*> 461*> \param[out] IWORK 462*> \verbatim 463*> IWORK is INTEGER array, dimension (N) 464*> \endverbatim 465*> 466*> \param[out] INFO 467*> \verbatim 468*> INFO is INTEGER 469*> = 0: Successful exit. The solution to every right-hand side is 470*> guaranteed. 471*> < 0: If INFO = -i, the i-th argument had an illegal value 472*> > 0 and <= N: U(INFO,INFO) is exactly zero. The factorization 473*> has been completed, but the factor U is exactly singular, so 474*> the solution and error bounds could not be computed. RCOND = 0 475*> is returned. 476*> = N+J: The solution corresponding to the Jth right-hand side is 477*> not guaranteed. The solutions corresponding to other right- 478*> hand sides K with K > J may not be guaranteed as well, but 479*> only the first such right-hand side is reported. If a small 480*> componentwise error is not requested (PARAMS(3) = 0.0) then 481*> the Jth right-hand side is the first with a normwise error 482*> bound that is not guaranteed (the smallest J such 483*> that ERR_BNDS_NORM(J,1) = 0.0). By default (PARAMS(3) = 1.0) 484*> the Jth right-hand side is the first with either a normwise or 485*> componentwise error bound that is not guaranteed (the smallest 486*> J such that either ERR_BNDS_NORM(J,1) = 0.0 or 487*> ERR_BNDS_COMP(J,1) = 0.0). See the definition of 488*> ERR_BNDS_NORM(:,1) and ERR_BNDS_COMP(:,1). To get information 489*> about all of the right-hand sides check ERR_BNDS_NORM or 490*> ERR_BNDS_COMP. 491*> \endverbatim 492* 493* Authors: 494* ======== 495* 496*> \author Univ. of Tennessee 497*> \author Univ. of California Berkeley 498*> \author Univ. of Colorado Denver 499*> \author NAG Ltd. 500* 501*> \ingroup realSYsolve 502* 503* ===================================================================== 504 SUBROUTINE SSYSVXX( FACT, UPLO, N, NRHS, A, LDA, AF, LDAF, IPIV, 505 $ EQUED, S, B, LDB, X, LDX, RCOND, RPVGRW, BERR, 506 $ N_ERR_BNDS, ERR_BNDS_NORM, ERR_BNDS_COMP, 507 $ NPARAMS, PARAMS, WORK, IWORK, INFO ) 508* 509* -- LAPACK driver routine -- 510* -- LAPACK is a software package provided by Univ. of Tennessee, -- 511* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- 512* 513* .. Scalar Arguments .. 514 CHARACTER EQUED, FACT, UPLO 515 INTEGER INFO, LDA, LDAF, LDB, LDX, N, NRHS, NPARAMS, 516 $ N_ERR_BNDS 517 REAL RCOND, RPVGRW 518* .. 519* .. Array Arguments .. 520 INTEGER IPIV( * ), IWORK( * ) 521 REAL A( LDA, * ), AF( LDAF, * ), B( LDB, * ), 522 $ X( LDX, * ), WORK( * ) 523 REAL S( * ), PARAMS( * ), BERR( * ), 524 $ ERR_BNDS_NORM( NRHS, * ), 525 $ ERR_BNDS_COMP( NRHS, * ) 526* .. 527* 528* ================================================================== 529* 530* .. Parameters .. 531 REAL ZERO, ONE 532 PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 ) 533 INTEGER FINAL_NRM_ERR_I, FINAL_CMP_ERR_I, BERR_I 534 INTEGER RCOND_I, NRM_RCOND_I, NRM_ERR_I, CMP_RCOND_I 535 INTEGER CMP_ERR_I, PIV_GROWTH_I 536 PARAMETER ( FINAL_NRM_ERR_I = 1, FINAL_CMP_ERR_I = 2, 537 $ BERR_I = 3 ) 538 PARAMETER ( RCOND_I = 4, NRM_RCOND_I = 5, NRM_ERR_I = 6 ) 539 PARAMETER ( CMP_RCOND_I = 7, CMP_ERR_I = 8, 540 $ PIV_GROWTH_I = 9 ) 541* .. 542* .. Local Scalars .. 543 LOGICAL EQUIL, NOFACT, RCEQU 544 INTEGER INFEQU, J 545 REAL AMAX, BIGNUM, SMIN, SMAX, SCOND, SMLNUM 546* .. 547* .. External Functions .. 548 EXTERNAL LSAME, SLAMCH, SLA_SYRPVGRW 549 LOGICAL LSAME 550 REAL SLAMCH, SLA_SYRPVGRW 551* .. 552* .. External Subroutines .. 553 EXTERNAL SSYEQUB, SSYTRF, SSYTRS, 554 $ SLACPY, SLAQSY, XERBLA, SLASCL2, SSYRFSX 555* .. 556* .. Intrinsic Functions .. 557 INTRINSIC MAX, MIN 558* .. 559* .. Executable Statements .. 560* 561 INFO = 0 562 NOFACT = LSAME( FACT, 'N' ) 563 EQUIL = LSAME( FACT, 'E' ) 564 SMLNUM = SLAMCH( 'Safe minimum' ) 565 BIGNUM = ONE / SMLNUM 566 IF( NOFACT .OR. EQUIL ) THEN 567 EQUED = 'N' 568 RCEQU = .FALSE. 569 ELSE 570 RCEQU = LSAME( EQUED, 'Y' ) 571 ENDIF 572* 573* Default is failure. If an input parameter is wrong or 574* factorization fails, make everything look horrible. Only the 575* pivot growth is set here, the rest is initialized in SSYRFSX. 576* 577 RPVGRW = ZERO 578* 579* Test the input parameters. PARAMS is not tested until SSYRFSX. 580* 581 IF( .NOT.NOFACT .AND. .NOT.EQUIL .AND. .NOT. 582 $ LSAME( FACT, 'F' ) ) THEN 583 INFO = -1 584 ELSE IF( .NOT.LSAME(UPLO, 'U') .AND. 585 $ .NOT.LSAME(UPLO, 'L') ) THEN 586 INFO = -2 587 ELSE IF( N.LT.0 ) THEN 588 INFO = -3 589 ELSE IF( NRHS.LT.0 ) THEN 590 INFO = -4 591 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN 592 INFO = -6 593 ELSE IF( LDAF.LT.MAX( 1, N ) ) THEN 594 INFO = -8 595 ELSE IF( LSAME( FACT, 'F' ) .AND. .NOT. 596 $ ( RCEQU .OR. LSAME( EQUED, 'N' ) ) ) THEN 597 INFO = -10 598 ELSE 599 IF ( RCEQU ) THEN 600 SMIN = BIGNUM 601 SMAX = ZERO 602 DO 10 J = 1, N 603 SMIN = MIN( SMIN, S( J ) ) 604 SMAX = MAX( SMAX, S( J ) ) 605 10 CONTINUE 606 IF( SMIN.LE.ZERO ) THEN 607 INFO = -11 608 ELSE IF( N.GT.0 ) THEN 609 SCOND = MAX( SMIN, SMLNUM ) / MIN( SMAX, BIGNUM ) 610 ELSE 611 SCOND = ONE 612 END IF 613 END IF 614 IF( INFO.EQ.0 ) THEN 615 IF( LDB.LT.MAX( 1, N ) ) THEN 616 INFO = -13 617 ELSE IF( LDX.LT.MAX( 1, N ) ) THEN 618 INFO = -15 619 END IF 620 END IF 621 END IF 622* 623 IF( INFO.NE.0 ) THEN 624 CALL XERBLA( 'SSYSVXX', -INFO ) 625 RETURN 626 END IF 627* 628 IF( EQUIL ) THEN 629* 630* Compute row and column scalings to equilibrate the matrix A. 631* 632 CALL SSYEQUB( UPLO, N, A, LDA, S, SCOND, AMAX, WORK, INFEQU ) 633 IF( INFEQU.EQ.0 ) THEN 634* 635* Equilibrate the matrix. 636* 637 CALL SLAQSY( UPLO, N, A, LDA, S, SCOND, AMAX, EQUED ) 638 RCEQU = LSAME( EQUED, 'Y' ) 639 END IF 640 END IF 641* 642* Scale the right-hand side. 643* 644 IF( RCEQU ) CALL SLASCL2( N, NRHS, S, B, LDB ) 645* 646 IF( NOFACT .OR. EQUIL ) THEN 647* 648* Compute the LDL^T or UDU^T factorization of A. 649* 650 CALL SLACPY( UPLO, N, N, A, LDA, AF, LDAF ) 651 CALL SSYTRF( UPLO, N, AF, LDAF, IPIV, WORK, 5*MAX(1,N), INFO ) 652* 653* Return if INFO is non-zero. 654* 655 IF( INFO.GT.0 ) THEN 656* 657* Pivot in column INFO is exactly 0 658* Compute the reciprocal pivot growth factor of the 659* leading rank-deficient INFO columns of A. 660* 661 IF ( N.GT.0 ) 662 $ RPVGRW = SLA_SYRPVGRW(UPLO, N, INFO, A, LDA, AF, 663 $ LDAF, IPIV, WORK ) 664 RETURN 665 END IF 666 END IF 667* 668* Compute the reciprocal pivot growth factor RPVGRW. 669* 670 IF ( N.GT.0 ) 671 $ RPVGRW = SLA_SYRPVGRW( UPLO, N, INFO, A, LDA, AF, LDAF, 672 $ IPIV, WORK ) 673* 674* Compute the solution matrix X. 675* 676 CALL SLACPY( 'Full', N, NRHS, B, LDB, X, LDX ) 677 CALL SSYTRS( UPLO, N, NRHS, AF, LDAF, IPIV, X, LDX, INFO ) 678* 679* Use iterative refinement to improve the computed solution and 680* compute error bounds and backward error estimates for it. 681* 682 CALL SSYRFSX( UPLO, EQUED, N, NRHS, A, LDA, AF, LDAF, IPIV, 683 $ S, B, LDB, X, LDX, RCOND, BERR, N_ERR_BNDS, ERR_BNDS_NORM, 684 $ ERR_BNDS_COMP, NPARAMS, PARAMS, WORK, IWORK, INFO ) 685* 686* Scale solutions. 687* 688 IF ( RCEQU ) THEN 689 CALL SLASCL2 ( N, NRHS, S, X, LDX ) 690 END IF 691* 692 RETURN 693* 694* End of SSYSVXX 695* 696 END 697