LAPACK 3.12.0
LAPACK: Linear Algebra PACKage
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◆ ztbsv()

subroutine ztbsv ( character  uplo,
character  trans,
character  diag,
integer  n,
integer  k,
complex*16, dimension(lda,*)  a,
integer  lda,
complex*16, dimension(*)  x,
integer  incx 
)

ZTBSV

Purpose:
 ZTBSV  solves one of the systems of equations

    A*x = b,   or   A**T*x = b,   or   A**H*x = b,

 where b and x are n element vectors and A is an n by n unit, or
 non-unit, upper or lower triangular band matrix, with ( k + 1 )
 diagonals.

 No test for singularity or near-singularity is included in this
 routine. Such tests must be performed before calling this routine.
Parameters
[in]UPLO
          UPLO is CHARACTER*1
           On entry, UPLO specifies whether the matrix is an upper or
           lower triangular matrix as follows:

              UPLO = 'U' or 'u'   A is an upper triangular matrix.

              UPLO = 'L' or 'l'   A is a lower triangular matrix.
[in]TRANS
          TRANS is CHARACTER*1
           On entry, TRANS specifies the equations to be solved as
           follows:

              TRANS = 'N' or 'n'   A*x = b.

              TRANS = 'T' or 't'   A**T*x = b.

              TRANS = 'C' or 'c'   A**H*x = b.
[in]DIAG
          DIAG is CHARACTER*1
           On entry, DIAG specifies whether or not A is unit
           triangular as follows:

              DIAG = 'U' or 'u'   A is assumed to be unit triangular.

              DIAG = 'N' or 'n'   A is not assumed to be unit
                                  triangular.
[in]N
          N is INTEGER
           On entry, N specifies the order of the matrix A.
           N must be at least zero.
[in]K
          K is INTEGER
           On entry with UPLO = 'U' or 'u', K specifies the number of
           super-diagonals of the matrix A.
           On entry with UPLO = 'L' or 'l', K specifies the number of
           sub-diagonals of the matrix A.
           K must satisfy  0 .le. K.
[in]A
          A is COMPLEX*16 array, dimension ( LDA, N )
           Before entry with UPLO = 'U' or 'u', the leading ( k + 1 )
           by n part of the array A must contain the upper triangular
           band part of the matrix of coefficients, supplied column by
           column, with the leading diagonal of the matrix in row
           ( k + 1 ) of the array, the first super-diagonal starting at
           position 2 in row k, and so on. The top left k by k triangle
           of the array A is not referenced.
           The following program segment will transfer an upper
           triangular band matrix from conventional full matrix storage
           to band storage:

                 DO 20, J = 1, N
                    M = K + 1 - J
                    DO 10, I = MAX( 1, J - K ), J
                       A( M + I, J ) = matrix( I, J )
              10    CONTINUE
              20 CONTINUE

           Before entry with UPLO = 'L' or 'l', the leading ( k + 1 )
           by n part of the array A must contain the lower triangular
           band part of the matrix of coefficients, supplied column by
           column, with the leading diagonal of the matrix in row 1 of
           the array, the first sub-diagonal starting at position 1 in
           row 2, and so on. The bottom right k by k triangle of the
           array A is not referenced.
           The following program segment will transfer a lower
           triangular band matrix from conventional full matrix storage
           to band storage:

                 DO 20, J = 1, N
                    M = 1 - J
                    DO 10, I = J, MIN( N, J + K )
                       A( M + I, J ) = matrix( I, J )
              10    CONTINUE
              20 CONTINUE

           Note that when DIAG = 'U' or 'u' the elements of the array A
           corresponding to the diagonal elements of the matrix are not
           referenced, but are assumed to be unity.
[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
           ( k + 1 ).
[in,out]X
          X is COMPLEX*16 array, dimension at least
           ( 1 + ( n - 1 )*abs( INCX ) ).
           Before entry, the incremented array X must contain the n
           element right-hand side vector b. On exit, X is overwritten
           with the solution vector x.
[in]INCX
          INCX is INTEGER
           On entry, INCX specifies the increment for the elements of
           X. INCX must not be zero.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Further Details:
  Level 2 Blas routine.

  -- 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 188 of file ztbsv.f.

189*
190* -- Reference BLAS level2 routine --
191* -- Reference BLAS is a software package provided by Univ. of Tennessee, --
192* -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
193*
194* .. Scalar Arguments ..
195 INTEGER INCX,K,LDA,N
196 CHARACTER DIAG,TRANS,UPLO
197* ..
198* .. Array Arguments ..
199 COMPLEX*16 A(LDA,*),X(*)
200* ..
201*
202* =====================================================================
203*
204* .. Parameters ..
205 COMPLEX*16 ZERO
206 parameter(zero= (0.0d+0,0.0d+0))
207* ..
208* .. Local Scalars ..
209 COMPLEX*16 TEMP
210 INTEGER I,INFO,IX,J,JX,KPLUS1,KX,L
211 LOGICAL NOCONJ,NOUNIT
212* ..
213* .. External Functions ..
214 LOGICAL LSAME
215 EXTERNAL lsame
216* ..
217* .. External Subroutines ..
218 EXTERNAL xerbla
219* ..
220* .. Intrinsic Functions ..
221 INTRINSIC dconjg,max,min
222* ..
223*
224* Test the input parameters.
225*
226 info = 0
227 IF (.NOT.lsame(uplo,'U') .AND. .NOT.lsame(uplo,'L')) THEN
228 info = 1
229 ELSE IF (.NOT.lsame(trans,'N') .AND.
230 + .NOT.lsame(trans,'T') .AND.
231 + .NOT.lsame(trans,'C')) THEN
232 info = 2
233 ELSE IF (.NOT.lsame(diag,'U') .AND.
234 + .NOT.lsame(diag,'N')) THEN
235 info = 3
236 ELSE IF (n.LT.0) THEN
237 info = 4
238 ELSE IF (k.LT.0) THEN
239 info = 5
240 ELSE IF (lda.LT. (k+1)) THEN
241 info = 7
242 ELSE IF (incx.EQ.0) THEN
243 info = 9
244 END IF
245 IF (info.NE.0) THEN
246 CALL xerbla('ZTBSV ',info)
247 RETURN
248 END IF
249*
250* Quick return if possible.
251*
252 IF (n.EQ.0) RETURN
253*
254 noconj = lsame(trans,'T')
255 nounit = lsame(diag,'N')
256*
257* Set up the start point in X if the increment is not unity. This
258* will be ( N - 1 )*INCX too small for descending loops.
259*
260 IF (incx.LE.0) THEN
261 kx = 1 - (n-1)*incx
262 ELSE IF (incx.NE.1) THEN
263 kx = 1
264 END IF
265*
266* Start the operations. In this version the elements of A are
267* accessed by sequentially with one pass through A.
268*
269 IF (lsame(trans,'N')) THEN
270*
271* Form x := inv( A )*x.
272*
273 IF (lsame(uplo,'U')) THEN
274 kplus1 = k + 1
275 IF (incx.EQ.1) THEN
276 DO 20 j = n,1,-1
277 IF (x(j).NE.zero) THEN
278 l = kplus1 - j
279 IF (nounit) x(j) = x(j)/a(kplus1,j)
280 temp = x(j)
281 DO 10 i = j - 1,max(1,j-k),-1
282 x(i) = x(i) - temp*a(l+i,j)
283 10 CONTINUE
284 END IF
285 20 CONTINUE
286 ELSE
287 kx = kx + (n-1)*incx
288 jx = kx
289 DO 40 j = n,1,-1
290 kx = kx - incx
291 IF (x(jx).NE.zero) THEN
292 ix = kx
293 l = kplus1 - j
294 IF (nounit) x(jx) = x(jx)/a(kplus1,j)
295 temp = x(jx)
296 DO 30 i = j - 1,max(1,j-k),-1
297 x(ix) = x(ix) - temp*a(l+i,j)
298 ix = ix - incx
299 30 CONTINUE
300 END IF
301 jx = jx - incx
302 40 CONTINUE
303 END IF
304 ELSE
305 IF (incx.EQ.1) THEN
306 DO 60 j = 1,n
307 IF (x(j).NE.zero) THEN
308 l = 1 - j
309 IF (nounit) x(j) = x(j)/a(1,j)
310 temp = x(j)
311 DO 50 i = j + 1,min(n,j+k)
312 x(i) = x(i) - temp*a(l+i,j)
313 50 CONTINUE
314 END IF
315 60 CONTINUE
316 ELSE
317 jx = kx
318 DO 80 j = 1,n
319 kx = kx + incx
320 IF (x(jx).NE.zero) THEN
321 ix = kx
322 l = 1 - j
323 IF (nounit) x(jx) = x(jx)/a(1,j)
324 temp = x(jx)
325 DO 70 i = j + 1,min(n,j+k)
326 x(ix) = x(ix) - temp*a(l+i,j)
327 ix = ix + incx
328 70 CONTINUE
329 END IF
330 jx = jx + incx
331 80 CONTINUE
332 END IF
333 END IF
334 ELSE
335*
336* Form x := inv( A**T )*x or x := inv( A**H )*x.
337*
338 IF (lsame(uplo,'U')) THEN
339 kplus1 = k + 1
340 IF (incx.EQ.1) THEN
341 DO 110 j = 1,n
342 temp = x(j)
343 l = kplus1 - j
344 IF (noconj) THEN
345 DO 90 i = max(1,j-k),j - 1
346 temp = temp - a(l+i,j)*x(i)
347 90 CONTINUE
348 IF (nounit) temp = temp/a(kplus1,j)
349 ELSE
350 DO 100 i = max(1,j-k),j - 1
351 temp = temp - dconjg(a(l+i,j))*x(i)
352 100 CONTINUE
353 IF (nounit) temp = temp/dconjg(a(kplus1,j))
354 END IF
355 x(j) = temp
356 110 CONTINUE
357 ELSE
358 jx = kx
359 DO 140 j = 1,n
360 temp = x(jx)
361 ix = kx
362 l = kplus1 - j
363 IF (noconj) THEN
364 DO 120 i = max(1,j-k),j - 1
365 temp = temp - a(l+i,j)*x(ix)
366 ix = ix + incx
367 120 CONTINUE
368 IF (nounit) temp = temp/a(kplus1,j)
369 ELSE
370 DO 130 i = max(1,j-k),j - 1
371 temp = temp - dconjg(a(l+i,j))*x(ix)
372 ix = ix + incx
373 130 CONTINUE
374 IF (nounit) temp = temp/dconjg(a(kplus1,j))
375 END IF
376 x(jx) = temp
377 jx = jx + incx
378 IF (j.GT.k) kx = kx + incx
379 140 CONTINUE
380 END IF
381 ELSE
382 IF (incx.EQ.1) THEN
383 DO 170 j = n,1,-1
384 temp = x(j)
385 l = 1 - j
386 IF (noconj) THEN
387 DO 150 i = min(n,j+k),j + 1,-1
388 temp = temp - a(l+i,j)*x(i)
389 150 CONTINUE
390 IF (nounit) temp = temp/a(1,j)
391 ELSE
392 DO 160 i = min(n,j+k),j + 1,-1
393 temp = temp - dconjg(a(l+i,j))*x(i)
394 160 CONTINUE
395 IF (nounit) temp = temp/dconjg(a(1,j))
396 END IF
397 x(j) = temp
398 170 CONTINUE
399 ELSE
400 kx = kx + (n-1)*incx
401 jx = kx
402 DO 200 j = n,1,-1
403 temp = x(jx)
404 ix = kx
405 l = 1 - j
406 IF (noconj) THEN
407 DO 180 i = min(n,j+k),j + 1,-1
408 temp = temp - a(l+i,j)*x(ix)
409 ix = ix - incx
410 180 CONTINUE
411 IF (nounit) temp = temp/a(1,j)
412 ELSE
413 DO 190 i = min(n,j+k),j + 1,-1
414 temp = temp - dconjg(a(l+i,j))*x(ix)
415 ix = ix - incx
416 190 CONTINUE
417 IF (nounit) temp = temp/dconjg(a(1,j))
418 END IF
419 x(jx) = temp
420 jx = jx - incx
421 IF ((n-j).GE.k) kx = kx - incx
422 200 CONTINUE
423 END IF
424 END IF
425 END IF
426*
427 RETURN
428*
429* End of ZTBSV
430*
subroutine xerbla(srname, info)
Definition cblat2.f:3285
logical function lsame(ca, cb)
LSAME
Definition lsame.f:48
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