LAPACK 3.12.1
LAPACK: Linear Algebra PACKage
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◆ dla_gbamv()

subroutine dla_gbamv ( integer trans,
integer m,
integer n,
integer kl,
integer ku,
double precision alpha,
double precision, dimension( ldab, * ) ab,
integer ldab,
double precision, dimension( * ) x,
integer incx,
double precision beta,
double precision, dimension( * ) y,
integer incy )

DLA_GBAMV performs a matrix-vector operation to calculate error bounds.

Download DLA_GBAMV + dependencies [TGZ] [ZIP] [TXT]

Purpose:
!>
!> DLA_GBAMV  performs one of the matrix-vector operations
!>
!>         y := alpha*abs(A)*abs(x) + beta*abs(y),
!>    or   y := alpha*abs(A)**T*abs(x) + beta*abs(y),
!>
!> where alpha and beta are scalars, x and y are vectors and A is an
!> m by n matrix.
!>
!> This function is primarily used in calculating error bounds.
!> To protect against underflow during evaluation, components in
!> the resulting vector are perturbed away from zero by (N+1)
!> times the underflow threshold.  To prevent unnecessarily large
!> errors for block-structure embedded in general matrices,
!>  zero components are not perturbed.  A zero
!> entry is considered  if all multiplications involved
!> in computing that entry have at least one zero multiplicand.
!>
Parameters
[in]TRANS
!>          TRANS is INTEGER
!>           On entry, TRANS specifies the operation to be performed as
!>           follows:
!>
!>             BLAS_NO_TRANS      y := alpha*abs(A)*abs(x) + beta*abs(y)
!>             BLAS_TRANS         y := alpha*abs(A**T)*abs(x) + beta*abs(y)
!>             BLAS_CONJ_TRANS    y := alpha*abs(A**T)*abs(x) + beta*abs(y)
!>
!>           Unchanged on exit.
!>
[in]M
!>          M is INTEGER
!>           On entry, M specifies the number of rows of the matrix A.
!>           M must be at least zero.
!>           Unchanged on exit.
!>
[in]N
!>          N is INTEGER
!>           On entry, N specifies the number of columns of the matrix A.
!>           N must be at least zero.
!>           Unchanged on exit.
!>
[in]KL
!>          KL is INTEGER
!>           The number of subdiagonals within the band of A.  KL >= 0.
!>
[in]KU
!>          KU is INTEGER
!>           The number of superdiagonals within the band of A.  KU >= 0.
!>
[in]ALPHA
!>          ALPHA is DOUBLE PRECISION
!>           On entry, ALPHA specifies the scalar alpha.
!>           Unchanged on exit.
!>
[in]AB
!>          AB is DOUBLE PRECISION array, dimension ( LDAB, n )
!>           Before entry, the leading m by n part of the array AB must
!>           contain the matrix of coefficients.
!>           Unchanged on exit.
!>
[in]LDAB
!>          LDAB is INTEGER
!>           On entry, LDA specifies the first dimension of AB as declared
!>           in the calling (sub) program. LDAB must be at least
!>           max( 1, m ).
!>           Unchanged on exit.
!>
[in]X
!>          X is DOUBLE PRECISION array, dimension
!>           ( 1 + ( n - 1 )*abs( INCX ) ) when TRANS = 'N' or 'n'
!>           and at least
!>           ( 1 + ( m - 1 )*abs( INCX ) ) otherwise.
!>           Before entry, the incremented array X must contain the
!>           vector x.
!>           Unchanged on exit.
!>
[in]INCX
!>          INCX is INTEGER
!>           On entry, INCX specifies the increment for the elements of
!>           X. INCX must not be zero.
!>           Unchanged on exit.
!>
[in]BETA
!>          BETA is DOUBLE PRECISION
!>           On entry, BETA specifies the scalar beta. When BETA is
!>           supplied as zero then Y need not be set on input.
!>           Unchanged on exit.
!>
[in,out]Y
!>          Y is DOUBLE PRECISION array, dimension
!>           ( 1 + ( m - 1 )*abs( INCY ) ) when TRANS = 'N' or 'n'
!>           and at least
!>           ( 1 + ( n - 1 )*abs( INCY ) ) otherwise.
!>           Before entry with BETA non-zero, the incremented array Y
!>           must contain the vector y. On exit, Y is overwritten by the
!>           updated vector y.
!>           If either m or n is zero, then Y not referenced and the function
!>           performs a quick return.
!>
[in]INCY
!>          INCY is INTEGER
!>           On entry, INCY specifies the increment for the elements of
!>           Y. INCY must not be zero.
!>           Unchanged on exit.
!>
!>  Level 2 Blas routine.
!>
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.

Definition at line 183 of file dla_gbamv.f.

185*
186* -- LAPACK computational routine --
187* -- LAPACK is a software package provided by Univ. of Tennessee, --
188* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
189*
190* .. Scalar Arguments ..
191 DOUBLE PRECISION ALPHA, BETA
192 INTEGER INCX, INCY, LDAB, M, N, KL, KU, TRANS
193* ..
194* .. Array Arguments ..
195 DOUBLE PRECISION AB( LDAB, * ), X( * ), Y( * )
196* ..
197*
198* =====================================================================
199*
200* .. Parameters ..
201 DOUBLE PRECISION ONE, ZERO
202 parameter( one = 1.0d+0, zero = 0.0d+0 )
203* ..
204* .. Local Scalars ..
205 LOGICAL SYMB_ZERO
206 DOUBLE PRECISION TEMP, SAFE1
207 INTEGER I, INFO, IY, J, JX, KX, KY, LENX, LENY, KD, KE
208* ..
209* .. External Subroutines ..
210 EXTERNAL xerbla, dlamch
211 DOUBLE PRECISION DLAMCH
212* ..
213* .. External Functions ..
214 EXTERNAL ilatrans
215 INTEGER ILATRANS
216* ..
217* .. Intrinsic Functions ..
218 INTRINSIC max, abs, sign
219* ..
220* .. Executable Statements ..
221*
222* Test the input parameters.
223*
224 info = 0
225 IF ( .NOT.( ( trans.EQ.ilatrans( 'N' ) )
226 $ .OR. ( trans.EQ.ilatrans( 'T' ) )
227 $ .OR. ( trans.EQ.ilatrans( 'C' ) ) ) ) THEN
228 info = 1
229 ELSE IF( m.LT.0 )THEN
230 info = 2
231 ELSE IF( n.LT.0 )THEN
232 info = 3
233 ELSE IF( kl.LT.0 .OR. kl.GT.m-1 ) THEN
234 info = 4
235 ELSE IF( ku.LT.0 .OR. ku.GT.n-1 ) THEN
236 info = 5
237 ELSE IF( ldab.LT.kl+ku+1 )THEN
238 info = 6
239 ELSE IF( incx.EQ.0 )THEN
240 info = 8
241 ELSE IF( incy.EQ.0 )THEN
242 info = 11
243 END IF
244 IF( info.NE.0 )THEN
245 CALL xerbla( 'DLA_GBAMV ', info )
246 RETURN
247 END IF
248*
249* Quick return if possible.
250*
251 IF( ( m.EQ.0 ).OR.( n.EQ.0 ).OR.
252 $ ( ( alpha.EQ.zero ).AND.( beta.EQ.one ) ) )
253 $ RETURN
254*
255* Set LENX and LENY, the lengths of the vectors x and y, and set
256* up the start points in X and Y.
257*
258 IF( trans.EQ.ilatrans( 'N' ) )THEN
259 lenx = n
260 leny = m
261 ELSE
262 lenx = m
263 leny = n
264 END IF
265 IF( incx.GT.0 )THEN
266 kx = 1
267 ELSE
268 kx = 1 - ( lenx - 1 )*incx
269 END IF
270 IF( incy.GT.0 )THEN
271 ky = 1
272 ELSE
273 ky = 1 - ( leny - 1 )*incy
274 END IF
275*
276* Set SAFE1 essentially to be the underflow threshold times the
277* number of additions in each row.
278*
279 safe1 = dlamch( 'Safe minimum' )
280 safe1 = (n+1)*safe1
281*
282* Form y := alpha*abs(A)*abs(x) + beta*abs(y).
283*
284* The O(M*N) SYMB_ZERO tests could be replaced by O(N) queries to
285* the inexact flag. Still doesn't help change the iteration order
286* to per-column.
287*
288 kd = ku + 1
289 ke = kl + 1
290 iy = ky
291 IF ( incx.EQ.1 ) THEN
292 IF( trans.EQ.ilatrans( 'N' ) )THEN
293 DO i = 1, leny
294 IF ( beta .EQ. zero ) THEN
295 symb_zero = .true.
296 y( iy ) = 0.0d+0
297 ELSE IF ( y( iy ) .EQ. zero ) THEN
298 symb_zero = .true.
299 ELSE
300 symb_zero = .false.
301 y( iy ) = beta * abs( y( iy ) )
302 END IF
303 IF ( alpha .NE. zero ) THEN
304 DO j = max( i-kl, 1 ), min( i+ku, lenx )
305 temp = abs( ab( kd+i-j, j ) )
306 symb_zero = symb_zero .AND.
307 $ ( x( j ) .EQ. zero .OR. temp .EQ. zero )
308
309 y( iy ) = y( iy ) + alpha*abs( x( j ) )*temp
310 END DO
311 END IF
312
313 IF ( .NOT.symb_zero )
314 $ y( iy ) = y( iy ) + sign( safe1, y( iy ) )
315 iy = iy + incy
316 END DO
317 ELSE
318 DO i = 1, leny
319 IF ( beta .EQ. zero ) THEN
320 symb_zero = .true.
321 y( iy ) = 0.0d+0
322 ELSE IF ( y( iy ) .EQ. zero ) THEN
323 symb_zero = .true.
324 ELSE
325 symb_zero = .false.
326 y( iy ) = beta * abs( y( iy ) )
327 END IF
328 IF ( alpha .NE. zero ) THEN
329 DO j = max( i-kl, 1 ), min( i+ku, lenx )
330 temp = abs( ab( ke-i+j, i ) )
331 symb_zero = symb_zero .AND.
332 $ ( x( j ) .EQ. zero .OR. temp .EQ. zero )
333
334 y( iy ) = y( iy ) + alpha*abs( x( j ) )*temp
335 END DO
336 END IF
337
338 IF ( .NOT.symb_zero )
339 $ y( iy ) = y( iy ) + sign( safe1, y( iy ) )
340 iy = iy + incy
341 END DO
342 END IF
343 ELSE
344 IF( trans.EQ.ilatrans( 'N' ) )THEN
345 DO i = 1, leny
346 IF ( beta .EQ. zero ) THEN
347 symb_zero = .true.
348 y( iy ) = 0.0d+0
349 ELSE IF ( y( iy ) .EQ. zero ) THEN
350 symb_zero = .true.
351 ELSE
352 symb_zero = .false.
353 y( iy ) = beta * abs( y( iy ) )
354 END IF
355 IF ( alpha .NE. zero ) THEN
356 jx = kx
357 DO j = max( i-kl, 1 ), min( i+ku, lenx )
358 temp = abs( ab( kd+i-j, j ) )
359 symb_zero = symb_zero .AND.
360 $ ( x( jx ) .EQ. zero .OR. temp .EQ. zero )
361
362 y( iy ) = y( iy ) + alpha*abs( x( jx ) )*temp
363 jx = jx + incx
364 END DO
365 END IF
366
367 IF ( .NOT.symb_zero )
368 $ y( iy ) = y( iy ) + sign( safe1, y( iy ) )
369
370 iy = iy + incy
371 END DO
372 ELSE
373 DO i = 1, leny
374 IF ( beta .EQ. zero ) THEN
375 symb_zero = .true.
376 y( iy ) = 0.0d+0
377 ELSE IF ( y( iy ) .EQ. zero ) THEN
378 symb_zero = .true.
379 ELSE
380 symb_zero = .false.
381 y( iy ) = beta * abs( y( iy ) )
382 END IF
383 IF ( alpha .NE. zero ) THEN
384 jx = kx
385 DO j = max( i-kl, 1 ), min( i+ku, lenx )
386 temp = abs( ab( ke-i+j, i ) )
387 symb_zero = symb_zero .AND.
388 $ ( x( jx ) .EQ. zero .OR. temp .EQ. zero )
389
390 y( iy ) = y( iy ) + alpha*abs( x( jx ) )*temp
391 jx = jx + incx
392 END DO
393 END IF
394
395 IF ( .NOT.symb_zero )
396 $ y( iy ) = y( iy ) + sign( safe1, y( iy ) )
397
398 iy = iy + incy
399 END DO
400 END IF
401
402 END IF
403*
404 RETURN
405*
406* End of DLA_GBAMV
407*
xerbla
subroutine xerbla(srname, info)
Definition cblat2.f:3285
ilatrans
integer function ilatrans(trans)
ILATRANS
Definition ilatrans.f:56
dlamch
double precision function dlamch(cmach)
DLAMCH
Definition dlamch.f:69
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