LAPACK  3.8.0
LAPACK: Linear Algebra PACKage

◆ slatm1()

subroutine slatm1 ( integer  MODE,
real  COND,
integer  IRSIGN,
integer  IDIST,
integer, dimension( 4 )  ISEED,
real, dimension( * )  D,
integer  N,
integer  INFO 
)

SLATM1

Purpose:
    SLATM1 computes the entries of D(1..N) as specified by
    MODE, COND and IRSIGN. IDIST and ISEED determine the generation
    of random numbers. SLATM1 is called by SLATMR to generate
    random test matrices for LAPACK programs.
Parameters
[in]MODE
          MODE is INTEGER
           On entry describes how D is to be computed:
           MODE = 0 means do not change D.
           MODE = 1 sets D(1)=1 and D(2:N)=1.0/COND
           MODE = 2 sets D(1:N-1)=1 and D(N)=1.0/COND
           MODE = 3 sets D(I)=COND**(-(I-1)/(N-1))
           MODE = 4 sets D(i)=1 - (i-1)/(N-1)*(1 - 1/COND)
           MODE = 5 sets D to random numbers in the range
                    ( 1/COND , 1 ) such that their logarithms
                    are uniformly distributed.
           MODE = 6 set D to random numbers from same distribution
                    as the rest of the matrix.
           MODE < 0 has the same meaning as ABS(MODE), except that
              the order of the elements of D is reversed.
           Thus if MODE is positive, D has entries ranging from
              1 to 1/COND, if negative, from 1/COND to 1,
           Not modified.
[in]COND
          COND is REAL
           On entry, used as described under MODE above.
           If used, it must be >= 1. Not modified.
[in]IRSIGN
          IRSIGN is INTEGER
           On entry, if MODE neither -6, 0 nor 6, determines sign of
           entries of D
           0 => leave entries of D unchanged
           1 => multiply each entry of D by 1 or -1 with probability .5
[in]IDIST
          IDIST is INTEGER
           On entry, IDIST specifies the type of distribution to be
           used to generate a random matrix .
           1 => UNIFORM( 0, 1 )
           2 => UNIFORM( -1, 1 )
           3 => NORMAL( 0, 1 )
           Not modified.
[in,out]ISEED
          ISEED is INTEGER array, dimension ( 4 )
           On entry ISEED specifies the seed of the random number
           generator. The random number generator uses a
           linear congruential sequence limited to small
           integers, and so should produce machine independent
           random numbers. The values of ISEED are changed on
           exit, and can be used in the next call to SLATM1
           to continue the same random number sequence.
           Changed on exit.
[in,out]D
          D is REAL array, dimension ( N )
           Array to be computed according to MODE, COND and IRSIGN.
           May be changed on exit if MODE is nonzero.
[in]N
          N is INTEGER
           Number of entries of D. Not modified.
[out]INFO
          INFO is INTEGER
            0  => normal termination
           -1  => if MODE not in range -6 to 6
           -2  => if MODE neither -6, 0 nor 6, and
                  IRSIGN neither 0 nor 1
           -3  => if MODE neither -6, 0 nor 6 and COND less than 1
           -4  => if MODE equals 6 or -6 and IDIST not in range 1 to 3
           -7  => if N negative
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
December 2016

Definition at line 137 of file slatm1.f.

137 *
138 * -- LAPACK auxiliary routine (version 3.7.0) --
139 * -- LAPACK is a software package provided by Univ. of Tennessee, --
140 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
141 * December 2016
142 *
143 * .. Scalar Arguments ..
144  INTEGER idist, info, irsign, mode, n
145  REAL cond
146 * ..
147 * .. Array Arguments ..
148  INTEGER iseed( 4 )
149  REAL d( * )
150 * ..
151 *
152 * =====================================================================
153 *
154 * .. Parameters ..
155  REAL one
156  parameter( one = 1.0e0 )
157  REAL half
158  parameter( half = 0.5e0 )
159 * ..
160 * .. Local Scalars ..
161  INTEGER i
162  REAL alpha, temp
163 * ..
164 * .. External Functions ..
165  REAL slaran
166  EXTERNAL slaran
167 * ..
168 * .. External Subroutines ..
169  EXTERNAL slarnv, xerbla
170 * ..
171 * .. Intrinsic Functions ..
172  INTRINSIC abs, exp, log, real
173 * ..
174 * .. Executable Statements ..
175 *
176 * Decode and Test the input parameters. Initialize flags & seed.
177 *
178  info = 0
179 *
180 * Quick return if possible
181 *
182  IF( n.EQ.0 )
183  $ RETURN
184 *
185 * Set INFO if an error
186 *
187  IF( mode.LT.-6 .OR. mode.GT.6 ) THEN
188  info = -1
189  ELSE IF( ( mode.NE.-6 .AND. mode.NE.0 .AND. mode.NE.6 ) .AND.
190  $ ( irsign.NE.0 .AND. irsign.NE.1 ) ) THEN
191  info = -2
192  ELSE IF( ( mode.NE.-6 .AND. mode.NE.0 .AND. mode.NE.6 ) .AND.
193  $ cond.LT.one ) THEN
194  info = -3
195  ELSE IF( ( mode.EQ.6 .OR. mode.EQ.-6 ) .AND.
196  $ ( idist.LT.1 .OR. idist.GT.3 ) ) THEN
197  info = -4
198  ELSE IF( n.LT.0 ) THEN
199  info = -7
200  END IF
201 *
202  IF( info.NE.0 ) THEN
203  CALL xerbla( 'SLATM1', -info )
204  RETURN
205  END IF
206 *
207 * Compute D according to COND and MODE
208 *
209  IF( mode.NE.0 ) THEN
210  GO TO ( 10, 30, 50, 70, 90, 110 )abs( mode )
211 *
212 * One large D value:
213 *
214  10 CONTINUE
215  DO 20 i = 1, n
216  d( i ) = one / cond
217  20 CONTINUE
218  d( 1 ) = one
219  GO TO 120
220 *
221 * One small D value:
222 *
223  30 CONTINUE
224  DO 40 i = 1, n
225  d( i ) = one
226  40 CONTINUE
227  d( n ) = one / cond
228  GO TO 120
229 *
230 * Exponentially distributed D values:
231 *
232  50 CONTINUE
233  d( 1 ) = one
234  IF( n.GT.1 ) THEN
235  alpha = cond**( -one / REAL( N-1 ) )
236  DO 60 i = 2, n
237  d( i ) = alpha**( i-1 )
238  60 CONTINUE
239  END IF
240  GO TO 120
241 *
242 * Arithmetically distributed D values:
243 *
244  70 CONTINUE
245  d( 1 ) = one
246  IF( n.GT.1 ) THEN
247  temp = one / cond
248  alpha = ( one-temp ) / REAL( n-1 )
249  DO 80 i = 2, n
250  d( i ) = REAL( n-i )*alpha + temp
251  80 CONTINUE
252  END IF
253  GO TO 120
254 *
255 * Randomly distributed D values on ( 1/COND , 1):
256 *
257  90 CONTINUE
258  alpha = log( one / cond )
259  DO 100 i = 1, n
260  d( i ) = exp( alpha*slaran( iseed ) )
261  100 CONTINUE
262  GO TO 120
263 *
264 * Randomly distributed D values from IDIST
265 *
266  110 CONTINUE
267  CALL slarnv( idist, iseed, n, d )
268 *
269  120 CONTINUE
270 *
271 * If MODE neither -6 nor 0 nor 6, and IRSIGN = 1, assign
272 * random signs to D
273 *
274  IF( ( mode.NE.-6 .AND. mode.NE.0 .AND. mode.NE.6 ) .AND.
275  $ irsign.EQ.1 ) THEN
276  DO 130 i = 1, n
277  temp = slaran( iseed )
278  IF( temp.GT.half )
279  $ d( i ) = -d( i )
280  130 CONTINUE
281  END IF
282 *
283 * Reverse if MODE < 0
284 *
285  IF( mode.LT.0 ) THEN
286  DO 140 i = 1, n / 2
287  temp = d( i )
288  d( i ) = d( n+1-i )
289  d( n+1-i ) = temp
290  140 CONTINUE
291  END IF
292 *
293  END IF
294 *
295  RETURN
296 *
297 * End of SLATM1
298 *
subroutine xerbla(SRNAME, INFO)
XERBLA
Definition: xerbla.f:62
subroutine slarnv(IDIST, ISEED, N, X)
SLARNV returns a vector of random numbers from a uniform or normal distribution.
Definition: slarnv.f:99
real function slaran(ISEED)
SLARAN
Definition: slaran.f:69
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