1*> \brief \b CGTT05 2* 3* =========== DOCUMENTATION =========== 4* 5* Online html documentation available at 6* http://www.netlib.org/lapack/explore-html/ 7* 8* Definition: 9* =========== 10* 11* SUBROUTINE CGTT05( TRANS, N, NRHS, DL, D, DU, B, LDB, X, LDX, 12* XACT, LDXACT, FERR, BERR, RESLTS ) 13* 14* .. Scalar Arguments .. 15* CHARACTER TRANS 16* INTEGER LDB, LDX, LDXACT, N, NRHS 17* .. 18* .. Array Arguments .. 19* REAL BERR( * ), FERR( * ), RESLTS( * ) 20* COMPLEX B( LDB, * ), D( * ), DL( * ), DU( * ), 21* $ X( LDX, * ), XACT( LDXACT, * ) 22* .. 23* 24* 25*> \par Purpose: 26* ============= 27*> 28*> \verbatim 29*> 30*> CGTT05 tests the error bounds from iterative refinement for the 31*> computed solution to a system of equations A*X = B, where A is a 32*> general tridiagonal matrix of order n and op(A) = A or A**T, 33*> depending on TRANS. 34*> 35*> RESLTS(1) = test of the error bound 36*> = norm(X - XACT) / ( norm(X) * FERR ) 37*> 38*> A large value is returned if this ratio is not less than one. 39*> 40*> RESLTS(2) = residual from the iterative refinement routine 41*> = the maximum of BERR / ( NZ*EPS + (*) ), where 42*> (*) = NZ*UNFL / (min_i (abs(op(A))*abs(X) +abs(b))_i ) 43*> and NZ = max. number of nonzeros in any row of A, plus 1 44*> \endverbatim 45* 46* Arguments: 47* ========== 48* 49*> \param[in] TRANS 50*> \verbatim 51*> TRANS is CHARACTER*1 52*> Specifies the form of the system of equations. 53*> = 'N': A * X = B (No transpose) 54*> = 'T': A**T * X = B (Transpose) 55*> = 'C': A**H * X = B (Conjugate transpose = Transpose) 56*> \endverbatim 57*> 58*> \param[in] N 59*> \verbatim 60*> N is INTEGER 61*> The number of rows of the matrices X and XACT. N >= 0. 62*> \endverbatim 63*> 64*> \param[in] NRHS 65*> \verbatim 66*> NRHS is INTEGER 67*> The number of columns of the matrices X and XACT. NRHS >= 0. 68*> \endverbatim 69*> 70*> \param[in] DL 71*> \verbatim 72*> DL is COMPLEX array, dimension (N-1) 73*> The (n-1) sub-diagonal elements of A. 74*> \endverbatim 75*> 76*> \param[in] D 77*> \verbatim 78*> D is COMPLEX array, dimension (N) 79*> The diagonal elements of A. 80*> \endverbatim 81*> 82*> \param[in] DU 83*> \verbatim 84*> DU is COMPLEX array, dimension (N-1) 85*> The (n-1) super-diagonal elements of A. 86*> \endverbatim 87*> 88*> \param[in] B 89*> \verbatim 90*> B is COMPLEX array, dimension (LDB,NRHS) 91*> The right hand side vectors for the system of linear 92*> equations. 93*> \endverbatim 94*> 95*> \param[in] LDB 96*> \verbatim 97*> LDB is INTEGER 98*> The leading dimension of the array B. LDB >= max(1,N). 99*> \endverbatim 100*> 101*> \param[in] X 102*> \verbatim 103*> X is COMPLEX array, dimension (LDX,NRHS) 104*> The computed solution vectors. Each vector is stored as a 105*> column of the matrix X. 106*> \endverbatim 107*> 108*> \param[in] LDX 109*> \verbatim 110*> LDX is INTEGER 111*> The leading dimension of the array X. LDX >= max(1,N). 112*> \endverbatim 113*> 114*> \param[in] XACT 115*> \verbatim 116*> XACT is COMPLEX array, dimension (LDX,NRHS) 117*> The exact solution vectors. Each vector is stored as a 118*> column of the matrix XACT. 119*> \endverbatim 120*> 121*> \param[in] LDXACT 122*> \verbatim 123*> LDXACT is INTEGER 124*> The leading dimension of the array XACT. LDXACT >= max(1,N). 125*> \endverbatim 126*> 127*> \param[in] FERR 128*> \verbatim 129*> FERR is REAL array, dimension (NRHS) 130*> The estimated forward error bounds for each solution vector 131*> X. If XTRUE is the true solution, FERR bounds the magnitude 132*> of the largest entry in (X - XTRUE) divided by the magnitude 133*> of the largest entry in X. 134*> \endverbatim 135*> 136*> \param[in] BERR 137*> \verbatim 138*> BERR is REAL array, dimension (NRHS) 139*> The componentwise relative backward error of each solution 140*> vector (i.e., the smallest relative change in any entry of A 141*> or B that makes X an exact solution). 142*> \endverbatim 143*> 144*> \param[out] RESLTS 145*> \verbatim 146*> RESLTS is REAL array, dimension (2) 147*> The maximum over the NRHS solution vectors of the ratios: 148*> RESLTS(1) = norm(X - XACT) / ( norm(X) * FERR ) 149*> RESLTS(2) = BERR / ( NZ*EPS + (*) ) 150*> \endverbatim 151* 152* Authors: 153* ======== 154* 155*> \author Univ. of Tennessee 156*> \author Univ. of California Berkeley 157*> \author Univ. of Colorado Denver 158*> \author NAG Ltd. 159* 160*> \ingroup complex_lin 161* 162* ===================================================================== 163 SUBROUTINE CGTT05( TRANS, N, NRHS, DL, D, DU, B, LDB, X, LDX, 164 $ XACT, LDXACT, FERR, BERR, RESLTS ) 165* 166* -- LAPACK test routine -- 167* -- LAPACK is a software package provided by Univ. of Tennessee, -- 168* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- 169* 170* .. Scalar Arguments .. 171 CHARACTER TRANS 172 INTEGER LDB, LDX, LDXACT, N, NRHS 173* .. 174* .. Array Arguments .. 175 REAL BERR( * ), FERR( * ), RESLTS( * ) 176 COMPLEX B( LDB, * ), D( * ), DL( * ), DU( * ), 177 $ X( LDX, * ), XACT( LDXACT, * ) 178* .. 179* 180* ===================================================================== 181* 182* .. Parameters .. 183 REAL ZERO, ONE 184 PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 ) 185* .. 186* .. Local Scalars .. 187 LOGICAL NOTRAN 188 INTEGER I, IMAX, J, K, NZ 189 REAL AXBI, DIFF, EPS, ERRBND, OVFL, TMP, UNFL, XNORM 190 COMPLEX ZDUM 191* .. 192* .. External Functions .. 193 LOGICAL LSAME 194 INTEGER ICAMAX 195 REAL SLAMCH 196 EXTERNAL LSAME, ICAMAX, SLAMCH 197* .. 198* .. Intrinsic Functions .. 199 INTRINSIC ABS, AIMAG, MAX, MIN, REAL 200* .. 201* .. Statement Functions .. 202 REAL CABS1 203* .. 204* .. Statement Function definitions .. 205 CABS1( ZDUM ) = ABS( REAL( ZDUM ) ) + ABS( AIMAG( ZDUM ) ) 206* .. 207* .. Executable Statements .. 208* 209* Quick exit if N = 0 or NRHS = 0. 210* 211 IF( N.LE.0 .OR. NRHS.LE.0 ) THEN 212 RESLTS( 1 ) = ZERO 213 RESLTS( 2 ) = ZERO 214 RETURN 215 END IF 216* 217 EPS = SLAMCH( 'Epsilon' ) 218 UNFL = SLAMCH( 'Safe minimum' ) 219 OVFL = ONE / UNFL 220 NOTRAN = LSAME( TRANS, 'N' ) 221 NZ = 4 222* 223* Test 1: Compute the maximum of 224* norm(X - XACT) / ( norm(X) * FERR ) 225* over all the vectors X and XACT using the infinity-norm. 226* 227 ERRBND = ZERO 228 DO 30 J = 1, NRHS 229 IMAX = ICAMAX( N, X( 1, J ), 1 ) 230 XNORM = MAX( CABS1( X( IMAX, J ) ), UNFL ) 231 DIFF = ZERO 232 DO 10 I = 1, N 233 DIFF = MAX( DIFF, CABS1( X( I, J )-XACT( I, J ) ) ) 234 10 CONTINUE 235* 236 IF( XNORM.GT.ONE ) THEN 237 GO TO 20 238 ELSE IF( DIFF.LE.OVFL*XNORM ) THEN 239 GO TO 20 240 ELSE 241 ERRBND = ONE / EPS 242 GO TO 30 243 END IF 244* 245 20 CONTINUE 246 IF( DIFF / XNORM.LE.FERR( J ) ) THEN 247 ERRBND = MAX( ERRBND, ( DIFF / XNORM ) / FERR( J ) ) 248 ELSE 249 ERRBND = ONE / EPS 250 END IF 251 30 CONTINUE 252 RESLTS( 1 ) = ERRBND 253* 254* Test 2: Compute the maximum of BERR / ( NZ*EPS + (*) ), where 255* (*) = NZ*UNFL / (min_i (abs(op(A))*abs(X) +abs(b))_i ) 256* 257 DO 60 K = 1, NRHS 258 IF( NOTRAN ) THEN 259 IF( N.EQ.1 ) THEN 260 AXBI = CABS1( B( 1, K ) ) + 261 $ CABS1( D( 1 ) )*CABS1( X( 1, K ) ) 262 ELSE 263 AXBI = CABS1( B( 1, K ) ) + 264 $ CABS1( D( 1 ) )*CABS1( X( 1, K ) ) + 265 $ CABS1( DU( 1 ) )*CABS1( X( 2, K ) ) 266 DO 40 I = 2, N - 1 267 TMP = CABS1( B( I, K ) ) + 268 $ CABS1( DL( I-1 ) )*CABS1( X( I-1, K ) ) + 269 $ CABS1( D( I ) )*CABS1( X( I, K ) ) + 270 $ CABS1( DU( I ) )*CABS1( X( I+1, K ) ) 271 AXBI = MIN( AXBI, TMP ) 272 40 CONTINUE 273 TMP = CABS1( B( N, K ) ) + CABS1( DL( N-1 ) )* 274 $ CABS1( X( N-1, K ) ) + CABS1( D( N ) )* 275 $ CABS1( X( N, K ) ) 276 AXBI = MIN( AXBI, TMP ) 277 END IF 278 ELSE 279 IF( N.EQ.1 ) THEN 280 AXBI = CABS1( B( 1, K ) ) + 281 $ CABS1( D( 1 ) )*CABS1( X( 1, K ) ) 282 ELSE 283 AXBI = CABS1( B( 1, K ) ) + 284 $ CABS1( D( 1 ) )*CABS1( X( 1, K ) ) + 285 $ CABS1( DL( 1 ) )*CABS1( X( 2, K ) ) 286 DO 50 I = 2, N - 1 287 TMP = CABS1( B( I, K ) ) + 288 $ CABS1( DU( I-1 ) )*CABS1( X( I-1, K ) ) + 289 $ CABS1( D( I ) )*CABS1( X( I, K ) ) + 290 $ CABS1( DL( I ) )*CABS1( X( I+1, K ) ) 291 AXBI = MIN( AXBI, TMP ) 292 50 CONTINUE 293 TMP = CABS1( B( N, K ) ) + CABS1( DU( N-1 ) )* 294 $ CABS1( X( N-1, K ) ) + CABS1( D( N ) )* 295 $ CABS1( X( N, K ) ) 296 AXBI = MIN( AXBI, TMP ) 297 END IF 298 END IF 299 TMP = BERR( K ) / ( NZ*EPS+NZ*UNFL / MAX( AXBI, NZ*UNFL ) ) 300 IF( K.EQ.1 ) THEN 301 RESLTS( 2 ) = TMP 302 ELSE 303 RESLTS( 2 ) = MAX( RESLTS( 2 ), TMP ) 304 END IF 305 60 CONTINUE 306* 307 RETURN 308* 309* End of CGTT05 310* 311 END 312