LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
Loading...
Searching...
No Matches

◆ sgbmv()

subroutine sgbmv ( character  trans,
integer  m,
integer  n,
integer  kl,
integer  ku,
real  alpha,
real, dimension(lda,*)  a,
integer  lda,
real, dimension(*)  x,
integer  incx,
real  beta,
real, dimension(*)  y,
integer  incy 
)

SGBMV

Purpose:
 SGBMV  performs one of the matrix-vector operations

    y := alpha*A*x + beta*y,   or   y := alpha*A**T*x + beta*y,

 where alpha and beta are scalars, x and y are vectors and A is an
 m by n band matrix, with kl sub-diagonals and ku super-diagonals.
Parameters
[in]TRANS
          TRANS is CHARACTER*1
           On entry, TRANS specifies the operation to be performed as
           follows:

              TRANS = 'N' or 'n'   y := alpha*A*x + beta*y.

              TRANS = 'T' or 't'   y := alpha*A**T*x + beta*y.

              TRANS = 'C' or 'c'   y := alpha*A**T*x + beta*y.
[in]M
          M is INTEGER
           On entry, M specifies the number of rows of the matrix A.
           M must be at least zero.
[in]N
          N is INTEGER
           On entry, N specifies the number of columns of the matrix A.
           N must be at least zero.
[in]KL
          KL is INTEGER
           On entry, KL specifies the number of sub-diagonals of the
           matrix A. KL must satisfy  0 .le. KL.
[in]KU
          KU is INTEGER
           On entry, KU specifies the number of super-diagonals of the
           matrix A. KU must satisfy  0 .le. KU.
[in]ALPHA
          ALPHA is REAL
           On entry, ALPHA specifies the scalar alpha.
[in]A
          A is REAL array, dimension ( LDA, N )
           Before entry, the leading ( kl + ku + 1 ) by n part of the
           array A must contain the matrix of coefficients, supplied
           column by column, with the leading diagonal of the matrix in
           row ( ku + 1 ) of the array, the first super-diagonal
           starting at position 2 in row ku, the first sub-diagonal
           starting at position 1 in row ( ku + 2 ), and so on.
           Elements in the array A that do not correspond to elements
           in the band matrix (such as the top left ku by ku triangle)
           are not referenced.
           The following program segment will transfer a band matrix
           from conventional full matrix storage to band storage:

                 DO 20, J = 1, N
                    K = KU + 1 - J
                    DO 10, I = MAX( 1, J - KU ), MIN( M, J + KL )
                       A( K + I, J ) = matrix( I, J )
              10    CONTINUE
              20 CONTINUE
[in]LDA
          LDA is INTEGER
           On entry, LDA specifies the first dimension of A as declared
           in the calling (sub) program. LDA must be at least
           ( kl + ku + 1 ).
[in]X
          X is REAL array, dimension at least
           ( 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.
[in]INCX
          INCX is INTEGER
           On entry, INCX specifies the increment for the elements of
           X. INCX must not be zero.
[in]BETA
          BETA is REAL
           On entry, BETA specifies the scalar beta. When BETA is
           supplied as zero then Y need not be set on input.
[in,out]Y
          Y is REAL array, dimension at least
           ( 1 + ( m - 1 )*abs( INCY ) ) when TRANS = 'N' or 'n'
           and at least
           ( 1 + ( n - 1 )*abs( INCY ) ) otherwise.
           Before entry, 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.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Further Details:
  Level 2 Blas routine.
  The vector and matrix arguments are not referenced when N = 0, or M = 0

  -- Written on 22-October-1986.
     Jack Dongarra, Argonne National Lab.
     Jeremy Du Croz, Nag Central Office.
     Sven Hammarling, Nag Central Office.
     Richard Hanson, Sandia National Labs.

Definition at line 186 of file sgbmv.f.

188*
189* -- Reference BLAS level2 routine --
190* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
191* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
192*
193* .. Scalar Arguments ..
194 REAL ALPHA,BETA
195 INTEGER INCX,INCY,KL,KU,LDA,M,N
196 CHARACTER TRANS
197* ..
198* .. Array Arguments ..
199 REAL A(LDA,*),X(*),Y(*)
200* ..
201*
202* =====================================================================
203*
204* .. Parameters ..
205 REAL ONE,ZERO
206 parameter(one=1.0e+0,zero=0.0e+0)
207* ..
208* .. Local Scalars ..
209 REAL TEMP
210 INTEGER I,INFO,IX,IY,J,JX,JY,K,KUP1,KX,KY,LENX,LENY
211* ..
212* .. External Functions ..
213 LOGICAL LSAME
214 EXTERNAL lsame
215* ..
216* .. External Subroutines ..
217 EXTERNAL xerbla
218* ..
219* .. Intrinsic Functions ..
220 INTRINSIC max,min
221* ..
222*
223* Test the input parameters.
224*
225 info = 0
226 IF (.NOT.lsame(trans,'N') .AND. .NOT.lsame(trans,'T') .AND.
227 + .NOT.lsame(trans,'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) THEN
234 info = 4
235 ELSE IF (ku.LT.0) THEN
236 info = 5
237 ELSE IF (lda.LT. (kl+ku+1)) THEN
238 info = 8
239 ELSE IF (incx.EQ.0) THEN
240 info = 10
241 ELSE IF (incy.EQ.0) THEN
242 info = 13
243 END IF
244 IF (info.NE.0) THEN
245 CALL xerbla('SGBMV ',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))) RETURN
253*
254* Set LENX and LENY, the lengths of the vectors x and y, and set
255* up the start points in X and Y.
256*
257 IF (lsame(trans,'N')) THEN
258 lenx = n
259 leny = m
260 ELSE
261 lenx = m
262 leny = n
263 END IF
264 IF (incx.GT.0) THEN
265 kx = 1
266 ELSE
267 kx = 1 - (lenx-1)*incx
268 END IF
269 IF (incy.GT.0) THEN
270 ky = 1
271 ELSE
272 ky = 1 - (leny-1)*incy
273 END IF
274*
275* Start the operations. In this version the elements of A are
276* accessed sequentially with one pass through the band part of A.
277*
278* First form y := beta*y.
279*
280 IF (beta.NE.one) THEN
281 IF (incy.EQ.1) THEN
282 IF (beta.EQ.zero) THEN
283 DO 10 i = 1,leny
284 y(i) = zero
285 10 CONTINUE
286 ELSE
287 DO 20 i = 1,leny
288 y(i) = beta*y(i)
289 20 CONTINUE
290 END IF
291 ELSE
292 iy = ky
293 IF (beta.EQ.zero) THEN
294 DO 30 i = 1,leny
295 y(iy) = zero
296 iy = iy + incy
297 30 CONTINUE
298 ELSE
299 DO 40 i = 1,leny
300 y(iy) = beta*y(iy)
301 iy = iy + incy
302 40 CONTINUE
303 END IF
304 END IF
305 END IF
306 IF (alpha.EQ.zero) RETURN
307 kup1 = ku + 1
308 IF (lsame(trans,'N')) THEN
309*
310* Form y := alpha*A*x + y.
311*
312 jx = kx
313 IF (incy.EQ.1) THEN
314 DO 60 j = 1,n
315 temp = alpha*x(jx)
316 k = kup1 - j
317 DO 50 i = max(1,j-ku),min(m,j+kl)
318 y(i) = y(i) + temp*a(k+i,j)
319 50 CONTINUE
320 jx = jx + incx
321 60 CONTINUE
322 ELSE
323 DO 80 j = 1,n
324 temp = alpha*x(jx)
325 iy = ky
326 k = kup1 - j
327 DO 70 i = max(1,j-ku),min(m,j+kl)
328 y(iy) = y(iy) + temp*a(k+i,j)
329 iy = iy + incy
330 70 CONTINUE
331 jx = jx + incx
332 IF (j.GT.ku) ky = ky + incy
333 80 CONTINUE
334 END IF
335 ELSE
336*
337* Form y := alpha*A**T*x + y.
338*
339 jy = ky
340 IF (incx.EQ.1) THEN
341 DO 100 j = 1,n
342 temp = zero
343 k = kup1 - j
344 DO 90 i = max(1,j-ku),min(m,j+kl)
345 temp = temp + a(k+i,j)*x(i)
346 90 CONTINUE
347 y(jy) = y(jy) + alpha*temp
348 jy = jy + incy
349 100 CONTINUE
350 ELSE
351 DO 120 j = 1,n
352 temp = zero
353 ix = kx
354 k = kup1 - j
355 DO 110 i = max(1,j-ku),min(m,j+kl)
356 temp = temp + a(k+i,j)*x(ix)
357 ix = ix + incx
358 110 CONTINUE
359 y(jy) = y(jy) + alpha*temp
360 jy = jy + incy
361 IF (j.GT.ku) kx = kx + incx
362 120 CONTINUE
363 END IF
364 END IF
365*
366 RETURN
367*
368* End of SGBMV
369*
subroutine xerbla(srname, info)
Definition cblat2.f:3285
logical function lsame(ca, cb)
LSAME
Definition lsame.f:48
Here is the call graph for this function:
Here is the caller graph for this function: