1: /*
2: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
3: SLEPc - Scalable Library for Eigenvalue Problem Computations
4: Copyright (c) 2002-, Universitat Politecnica de Valencia, Spain
6: This file is part of SLEPc.
7: SLEPc is distributed under a 2-clause BSD license (see LICENSE).
8: - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
9: */
10: /*
11: BDC - Block-divide and conquer (see description in README file)
12: */
14: #include <slepc/private/dsimpl.h> 15: #include <slepcblaslapack.h> 17: PetscErrorCode BDC_dsbtdc_(const char *jobz,const char *jobacc,PetscBLASInt n, 18: PetscBLASInt nblks,PetscBLASInt *ksizes,PetscReal *d,PetscBLASInt l1d, 19: PetscBLASInt l2d,PetscReal *e,PetscBLASInt l1e,PetscBLASInt l2e,PetscReal tol, 20: PetscReal tau1,PetscReal tau2,PetscReal *ev,PetscReal *z,PetscBLASInt ldz, 21: PetscReal *work,PetscBLASInt lwork,PetscBLASInt *iwork,PetscBLASInt liwork, 22: PetscReal *mingap,PetscBLASInt *mingapi,PetscBLASInt *info, 23: PetscBLASInt jobz_len,PetscBLASInt jobacc_len) 24: {
25: /* -- Routine written in LAPACK Version 3.0 style -- */
26: /* *************************************************** */
27: /* Written by */
28: /* Michael Moldaschl and Wilfried Gansterer */
29: /* University of Vienna */
30: /* last modification: March 28, 2014 */
32: /* Small adaptations of original code written by */
33: /* Wilfried Gansterer and Bob Ward, */
34: /* Department of Computer Science, University of Tennessee */
35: /* see https://doi.org/10.1137/S1064827501399432 */
36: /* *************************************************** */
38: /* Purpose */
39: /* ======= */
41: /* DSBTDC computes approximations to all eigenvalues and eigenvectors */
42: /* of a symmetric block tridiagonal matrix using the divide and */
43: /* conquer method with lower rank approximations to the subdiagonal blocks. */
45: /* This code makes very mild assumptions about floating point */
46: /* arithmetic. It will work on machines with a guard digit in */
47: /* add/subtract, or on those binary machines without guard digits */
48: /* which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or Cray-2. */
49: /* It could conceivably fail on hexadecimal or decimal machines */
50: /* without guard digits, but we know of none. See DLAED3M for details. */
52: /* Arguments */
53: /* ========= */
55: /* JOBZ (input) CHARACTER*1 */
56: /* = 'N': Compute eigenvalues only (not implemented); */
57: /* = 'D': Compute eigenvalues and eigenvectors. Eigenvectors */
58: /* are accumulated in the divide-and-conquer process. */
60: /* JOBACC (input) CHARACTER*1 */
61: /* = 'A' ("automatic"): The accuracy parameters TAU1 and TAU2 */
62: /* are determined automatically from the */
63: /* parameter TOL according to the analytical */
64: /* bounds. In that case the input values of */
65: /* TAU1 and TAU2 are irrelevant (ignored). */
66: /* = 'M' ("manual"): The input values of the accuracy parameters */
67: /* TAU1 and TAU2 are used. In that case the input */
68: /* value of the parameter TOL is irrelevant */
69: /* (ignored). */
71: /* N (input) INTEGER */
72: /* The dimension of the symmetric block tridiagonal matrix. */
73: /* N >= 1. */
75: /* NBLKS (input) INTEGER, 1 <= NBLKS <= N */
76: /* The number of diagonal blocks in the matrix. */
78: /* KSIZES (input) INTEGER array, dimension (NBLKS) */
79: /* The dimensions of the square diagonal blocks from top left */
80: /* to bottom right. KSIZES(I) >= 1 for all I, and the sum of */
81: /* KSIZES(I) for I = 1 to NBLKS has to be equal to N. */
83: /* D (input) DOUBLE PRECISION array, dimension (L1D,L2D,NBLKS) */
84: /* The lower triangular elements of the symmetric diagonal */
85: /* blocks of the block tridiagonal matrix. The elements of the top */
86: /* left diagonal block, which is of dimension KSIZES(1), have to */
87: /* be placed in D(*,*,1); the elements of the next diagonal */
88: /* block, which is of dimension KSIZES(2), have to be placed in */
89: /* D(*,*,2); etc. */
91: /* L1D (input) INTEGER */
92: /* The leading dimension of the array D. L1D >= max(3,KMAX), */
93: /* where KMAX is the dimension of the largest diagonal block, */
94: /* i.e., KMAX = max_I (KSIZES(I)). */
96: /* L2D (input) INTEGER */
97: /* The second dimension of the array D. L2D >= max(3,KMAX), */
98: /* where KMAX is as stated in L1D above. */
100: /* E (input) DOUBLE PRECISION array, dimension (L1E,L2E,NBLKS-1) */
101: /* The elements of the subdiagonal blocks of the */
102: /* block tridiagonal matrix. The elements of the top left */
103: /* subdiagonal block, which is KSIZES(2) x KSIZES(1), have to be */
104: /* placed in E(*,*,1); the elements of the next subdiagonal block, */
105: /* which is KSIZES(3) x KSIZES(2), have to be placed in E(*,*,2); etc. */
106: /* During runtime, the original contents of E(*,*,K) is */
107: /* overwritten by the singular vectors and singular values of */
108: /* the lower rank representation. */
110: /* L1E (input) INTEGER */
111: /* The leading dimension of the array E. L1E >= max(3,2*KMAX+1), */
112: /* where KMAX is as stated in L1D above. The size of L1E enables */
113: /* the storage of ALL singular vectors and singular values for */
114: /* the corresponding off-diagonal block in E(*,*,K) and therefore */
115: /* there are no restrictions on the rank of the approximation */
116: /* (only the "natural" restriction */
117: /* RANK(K) .LE. MIN(KSIZES(K),KSIZES(K+1))). */
119: /* L2E (input) INTEGER */
120: /* The second dimension of the array E. L2E >= max(3,2*KMAX+1), */
121: /* where KMAX is as stated in L1D above. The size of L2E enables */
122: /* the storage of ALL singular vectors and singular values for */
123: /* the corresponding off-diagonal block in E(*,*,K) and therefore */
124: /* there are no restrictions on the rank of the approximation */
125: /* (only the "natural" restriction */
126: /* RANK(K) .LE. MIN(KSIZES(K),KSIZES(K+1))). */
128: /* TOL (input) DOUBLE PRECISION, TOL.LE.TOLMAX */
129: /* User specified tolerance for the residuals of the computed */
130: /* eigenpairs. If (JOBACC.EQ.'A') then it is used to determine */
131: /* TAU1 and TAU2; ignored otherwise. */
132: /* If (TOL.LT.40*EPS .AND. JOBACC.EQ.'A') then TAU1 is set to machine */
133: /* epsilon and TAU2 is set to the standard deflation tolerance from */
134: /* LAPACK. */
136: /* TAU1 (input) DOUBLE PRECISION, TAU1.LE.TOLMAX/2 */
137: /* User specified tolerance for determining the rank of the */
138: /* lower rank approximations to the off-diagonal blocks. */
139: /* The rank for each off-diagonal block is determined such that */
140: /* the resulting absolute eigenvalue error is less than or equal */
141: /* to TAU1. */
142: /* If (JOBACC.EQ.'A') then TAU1 is determined automatically from */
143: /* TOL and the input value is ignored. */
144: /* If (JOBACC.EQ.'M' .AND. TAU1.LT.20*EPS) then TAU1 is set to */
145: /* machine epsilon. */
147: /* TAU2 (input) DOUBLE PRECISION, TAU2.LE.TOLMAX/2 */
148: /* User specified deflation tolerance for the routine DIBTDC. */
149: /* If (1.0D-1.GT.TAU2.GT.20*EPS) then TAU2 is used as */
150: /* the deflation tolerance in DSRTDF (EPS is the machine epsilon). */
151: /* If (TAU2.LE.20*EPS) then the standard deflation tolerance from */
152: /* LAPACK is used as the deflation tolerance in DSRTDF. */
153: /* If (JOBACC.EQ.'A') then TAU2 is determined automatically from */
154: /* TOL and the input value is ignored. */
155: /* If (JOBACC.EQ.'M' .AND. TAU2.LT.20*EPS) then TAU2 is set to */
156: /* the standard deflation tolerance from LAPACK. */
158: /* EV (output) DOUBLE PRECISION array, dimension (N) */
159: /* If INFO = 0, then EV contains the computed eigenvalues of the */
160: /* symmetric block tridiagonal matrix in ascending order. */
162: /* Z (output) DOUBLE PRECISION array, dimension (LDZ,N) */
163: /* If (JOBZ.EQ.'D' .AND. INFO = 0) */
164: /* then Z contains the orthonormal eigenvectors of the symmetric */
165: /* block tridiagonal matrix computed by the routine DIBTDC */
166: /* (accumulated in the divide-and-conquer process). */
167: /* If (-199 < INFO < -99) then Z contains the orthonormal */
168: /* eigenvectors of the symmetric block tridiagonal matrix, */
169: /* computed without divide-and-conquer (quick returns). */
170: /* Otherwise not referenced. */
172: /* LDZ (input) INTEGER */
173: /* The leading dimension of the array Z. LDZ >= max(1,N). */
175: /* WORK (workspace/output) DOUBLE PRECISION array, dimension (LWORK) */
177: /* LWORK (input) INTEGER */
178: /* The dimension of the array WORK. */
179: /* If NBLKS.EQ.1, then LWORK has to be at least 2N^2+6N+1 */
180: /* (for the call of DSYEVD). */
181: /* If NBLKS.GE.2 and (JOBZ.EQ.'D') then the absolute minimum */
182: /* required for DIBTDC is (N**2 + 3*N). This will not always */
183: /* suffice, though, the routine will return a corresponding */
184: /* error code and report how much work space was missing (see */
185: /* INFO). */
186: /* In order to guarantee correct results in all cases where */
187: /* NBLKS.GE.2, LWORK must be at least (2*N**2 + 3*N). */
189: /* IWORK (workspace/output) INTEGER array, dimension (LIWORK) */
191: /* LIWORK (input) INTEGER */
192: /* The dimension of the array IWORK. */
193: /* LIWORK must be at least (5*N + 5*NBLKS - 1) (for DIBTDC) */
194: /* Note that this should also suffice for the call of DSYEVD on a */
195: /* diagonal block which requires (5*KMAX + 3). */
197: /* MINGAP (output) DOUBLE PRECISION */
198: /* The minimum "gap" between the approximate eigenvalues */
199: /* computed, i.e., MIN( ABS(EV(I+1)-EV(I)) for I=1,2,..., N-1 */
200: /* IF (MINGAP.LE.TOL/10) THEN a warning flag is returned in INFO, */
201: /* because the computed eigenvectors may be unreliable individually */
202: /* (only the subspaces spanned are approximated reliably). */
204: /* MINGAPI (output) INTEGER */
205: /* Index I where the minimum gap in the spectrum occurred. */
207: /* INFO (output) INTEGER */
208: /* = 0: successful exit, no special cases occurred. */
209: /* < -200: not enough workspace. Space for ABS(INFO + 200) */
210: /* numbers is required in addition to the workspace provided, */
211: /* otherwise some of the computed eigenvectors will be incorrect. */
212: /* < -99, > -199: successful exit, but quick returns. */
213: /* if INFO = -100, successful exit, but the input matrix */
214: /* was the zero matrix and no */
215: /* divide-and-conquer was performed */
216: /* if INFO = -101, successful exit, but N was 1 and no */
217: /* divide-and-conquer was performed */
218: /* if INFO = -102, successful exit, but only a single */
219: /* dense block. Standard dense solver */
220: /* was called, no divide-and-conquer was */
221: /* performed */
222: /* if INFO = -103, successful exit, but warning that */
223: /* MINGAP.LE.TOL/10 and therefore the */
224: /* eigenvectors corresponding to close */
225: /* approximate eigenvalues may individually */
226: /* be unreliable (although taken together they */
227: /* do approximate the corresponding subspace to */
228: /* the desired accuracy) */
229: /* = -99: error in the preprocessing in DIBTDC (when determining */
230: /* the merging order). */
231: /* < 0, > -99: illegal arguments. */
232: /* if INFO = -i, the i-th argument had an illegal value. */
233: /* > 0: The algorithm failed to compute an eigenvalue while */
234: /* working on the submatrix lying in rows and columns */
235: /* INFO/(N+1) through mod(INFO,N+1). */
237: /* Further Details */
238: /* =============== */
240: /* Small modifications of code written by */
241: /* Wilfried Gansterer and Bob Ward, */
242: /* Department of Computer Science, University of Tennessee */
243: /* see https://doi.org/10.1137/S1064827501399432 */
245: /* Based on the design of the LAPACK code sstedc.f written by Jeff */
246: /* Rutter, Computer Science Division, University of California at */
247: /* Berkeley, and modified by Francoise Tisseur, University of Tennessee. */
249: /* ===================================================================== */
251: /* .. Parameters .. */
253: #define TOLMAX 0.1255: /* TOLMAX .... upper bound for tolerances TOL, TAU1, TAU2 */
256: /* NOTE: in the routine DIBTDC, the value */
257: /* 1.D-1 is hardcoded for TOLMAX ! */
259: PetscBLASInt i, j, k, i1, iwspc, lwmin, start;
260: PetscBLASInt ii, ip, nk, rk, np, iu, rp1, ldu;
261: PetscBLASInt ksk, ivt, iend, kchk=0, kmax=0, one=1, zero=0;
262: PetscBLASInt ldvt, ksum=0, kskp1, spneed, nrblks, liwmin, isvals;
263: PetscReal p, d2, eps, dmax, emax, done = 1.0;
264: PetscReal dnrm, tiny, anorm, exdnrm=0, dropsv, absdiff;
266: PetscFunctionBegin;
267: /* Determine machine epsilon. */
268: eps = LAPACKlamch_("Epsilon");
270: *info = 0;
272: if (*(unsigned char *)jobz != 'N' && *(unsigned char *)jobz != 'D') *info = -1;
273: else if (*(unsigned char *)jobacc != 'A' && *(unsigned char *)jobacc != 'M') *info = -2;
274: else if (n < 1) *info = -3;
275: else if (nblks < 1 || nblks > n) *info = -4;
276: if (*info == 0) {
277: for (k = 0; k < nblks; ++k) {
278: ksk = ksizes[k];
279: ksum += ksk;
280: if (ksk > kmax) kmax = ksk;
281: if (ksk < 1) kchk = 1;
282: }
283: if (nblks == 1) lwmin = 2*n*n + n*6 + 1;
284: else lwmin = n*n + n*3;
285: liwmin = n * 5 + nblks * 5 - 4;
286: if (ksum != n || kchk == 1) *info = -5;
287: else if (l1d < PetscMax(3,kmax)) *info = -7;
288: else if (l2d < PetscMax(3,kmax)) *info = -8;
289: else if (l1e < PetscMax(3,2*kmax+1)) *info = -10;
290: else if (l2e < PetscMax(3,2*kmax+1)) *info = -11;
291: else if (*(unsigned char *)jobacc == 'A' && tol > TOLMAX) *info = -12;
292: else if (*(unsigned char *)jobacc == 'M' && tau1 > TOLMAX/2) *info = -13;
293: else if (*(unsigned char *)jobacc == 'M' && tau2 > TOLMAX/2) *info = -14;
294: else if (ldz < PetscMax(1,n)) *info = -17;
295: else if (lwork < lwmin) *info = -19;
296: else if (liwork < liwmin) *info = -21;
297: }
299: PetscCheck(!*info,PETSC_COMM_SELF,PETSC_ERR_ARG_WRONG,"Wrong argument %" PetscBLASInt_FMT " in DSBTDC",-(*info));
301: /* Quick return if possible */
303: if (n == 1) {
304: ev[0] = d[0]; z[0] = 1.;
305: *info = -101;
306: PetscFunctionReturn(PETSC_SUCCESS);
307: }
309: /* If NBLKS is equal to 1, then solve the problem with standard */
310: /* dense solver (in this case KSIZES(1) = N). */
312: if (nblks == 1) {
313: for (i = 0; i < n; ++i) {
314: for (j = 0; j <= i; ++j) {
315: z[i + j*ldz] = d[i + j*l1d];
316: }
317: }
318: PetscCallBLAS("LAPACKsyevd",LAPACKsyevd_("V", "L", &n, z, &ldz, ev, work, &lwork, iwork, &liwork, info));
319: SlepcCheckLapackInfo("syevd",*info);
320: *info = -102;
321: PetscFunctionReturn(PETSC_SUCCESS);
322: }
324: /* determine the accuracy parameters (if requested) */
326: if (*(unsigned char *)jobacc == 'A') {
327: tau1 = tol / 2;
328: if (tau1 < eps * 20) tau1 = eps;
329: tau2 = tol / 2;
330: }
332: /* Initialize Z as the identity matrix */
334: if (*(unsigned char *)jobz == 'D') {
335: for (j=0;j<n;j++) for (i=0;i<n;i++) z[i+j*ldz] = 0.0;
336: for (i=0;i<n;i++) z[i+i*ldz] = 1.0;
337: }
339: /* Determine the off-diagonal ranks, form and store the lower rank */
340: /* approximations based on the tolerance parameters, the */
341: /* RANK(K) largest singular values and the associated singular */
342: /* vectors of each subdiagonal block. Also find the maximum norm of */
343: /* the subdiagonal blocks (in EMAX). */
345: /* Compute SVDs of the subdiagonal blocks.... */
347: /* EMAX .... maximum norm of the off-diagonal blocks */
349: emax = 0.;
350: for (k = 0; k < nblks-1; ++k) {
351: ksk = ksizes[k];
352: kskp1 = ksizes[k+1];
353: isvals = 0;
355: /* Note that min(KSKP1,KSK).LE.N/2 (equality possible for */
356: /* NBLKS=2), and therefore storing the singular values requires */
357: /* at most N/2 entries of the * array WORK. */
359: iu = isvals + n / 2;
360: ivt = isvals + n / 2;
362: /* Call of DGESVD: The space for U is not referenced, since */
363: /* JOBU='O' and therefore this portion of the array WORK */
364: /* is not referenced for U. */
366: ldu = kskp1;
367: ldvt = PetscMin(kskp1,ksk);
368: iwspc = ivt + n * n / 2;
370: /* Note that the minimum workspace required for this call */
371: /* of DGESVD is: N/2 for storing the singular values + N**2/2 for */
372: /* storing V^T + 5*N/2 workspace = N**2/2 + 3*N. */
374: i1 = lwork - iwspc;
375: PetscCallBLAS("LAPACKgesvd",LAPACKgesvd_("O", "S", &kskp1, &ksk,
376: &e[k*l1e*l2e], &l1e, &work[isvals],
377: &work[iu], &ldu, &work[ivt], &ldvt, &work[iwspc], &i1, info));
378: SlepcCheckLapackInfo("gesvd",*info);
380: /* Note that after the return from DGESVD U is stored in */
381: /* E(*,*,K), and V^{\top} is stored in WORK(IVT, IVT+1, ....) */
383: /* determine the ranks RANK() for the approximations */
385: rk = PetscMin(ksk,kskp1);
386: L8:
387: dropsv = work[isvals - 1 + rk];
389: if (dropsv * 2. <= tau1) {
391: /* the error caused by dropping singular value RK is */
392: /* small enough, try to reduce the rank by one more */
394: if (--rk > 0) goto L8;
395: else iwork[k] = 0;
396: } else {
398: /* the error caused by dropping singular value RK is */
399: /* too large already, RK is the rank required to achieve the */
400: /* desired accuracy */
402: iwork[k] = rk;
403: }
405: /* ************************************************************************** */
407: /* Store the first RANK(K) terms of the SVD of the current */
408: /* off-diagonal block. */
409: /* NOTE that here it is required that L1E, L2E >= 2*KMAX+1 in order */
410: /* to have enough space for storing singular vectors and values up */
411: /* to the full SVD of an off-diagonal block !!!! */
413: /* u1-u_RANK(K) is already contained in E(:,1:RANK(K),K) (as a */
414: /* result of the call of DGESVD !), the sigma1-sigmaK are to be */
415: /* stored in E(1:RANK(K),RANK(K)+1,K), and v1-v_RANK(K) are to be */
416: /* stored in E(:,RANK(K)+2:2*RANK(K)+1,K) */
418: rp1 = iwork[k];
419: for (j = 0; j < iwork[k]; ++j) {
421: /* store sigma_J in E(J,RANK(K)+1,K) */
423: e[j + (rp1 + k*l2e)* l1e] = work[isvals + j];
425: /* update maximum norm of subdiagonal blocks */
427: if (e[j + (rp1 + k*l2e)*l1e] > emax) {
428: emax = e[j + (rp1 + k*l2e)*l1e];
429: }
431: /* store v_J in E(:,RANK(K)+1+J,K) */
432: /* (note that WORK contains V^{\top} and therefore */
433: /* we need to read rowwise !) */
435: for (i = 1; i <= ksk; ++i) {
436: e[i-1 + (rp1+j+1 + k*l2e)*l1e] = work[ivt+j + (i-1)*ldvt];
437: }
438: }
440: }
442: /* Compute the maximum norm of diagonal blocks and store the norm */
443: /* of each diagonal block in E(RP1,RP1,K) (after the singular values); */
444: /* store the norm of the last diagonal block in EXDNRM. */
446: /* DMAX .... maximum one-norm of the diagonal blocks */
448: dmax = 0.;
449: for (k = 0; k < nblks; ++k) {
450: rp1 = iwork[k];
452: /* compute the one-norm of diagonal block K */
454: dnrm = LAPACKlansy_("1", "L", &ksizes[k], &d[k*l1d*l2d], &l1d, work);
455: if (k+1 == nblks) exdnrm = dnrm;
456: else e[rp1 + (rp1 + k*l2e)*l1e] = dnrm;
457: if (dnrm > dmax) dmax = dnrm;
458: }
460: /* Check for zero matrix. */
462: if (emax == 0. && dmax == 0.) {
463: for (i = 0; i < n; ++i) ev[i] = 0.;
464: *info = -100;
465: PetscFunctionReturn(PETSC_SUCCESS);
466: }
468: /* **************************************************************** */
470: /* ....Identify irreducible parts of the block tridiagonal matrix */
471: /* [while (START <= NBLKS)].... */
473: start = 0;
474: np = 0;
475: L10:
476: if (start < nblks) {
478: /* Let IEND be the number of the next subdiagonal block such that */
479: /* its RANK is 0 or IEND = NBLKS if no such subdiagonal exists. */
480: /* The matrix identified by the elements between the diagonal block START */
481: /* and the diagonal block IEND constitutes an independent (irreducible) */
482: /* sub-problem. */
484: iend = start;
486: L20:
487: if (iend < nblks) {
488: rk = iwork[iend];
490: /* NOTE: if RANK(IEND).EQ.0 then decoupling happens due to */
491: /* reduced accuracy requirements ! (because in this case */
492: /* we would not merge the corresponding two diagonal blocks) */
494: /* NOTE: seems like any combination may potentially happen: */
495: /* (i) RANK = 0 but no decoupling due to small norm of */
496: /* off-diagonal block (corresponding diagonal blocks */
497: /* also have small norm) as well as */
498: /* (ii) RANK > 0 but decoupling due to small norm of */
499: /* off-diagonal block (corresponding diagonal blocks */
500: /* have very large norm) */
501: /* case (i) is ruled out by checking for RANK = 0 above */
502: /* (we decide to decouple all the time when the rank */
503: /* of an off-diagonal block is zero, independently of */
504: /* the norms of the corresponding diagonal blocks. */
506: if (rk > 0) {
508: /* check for decoupling due to small norm of off-diagonal block */
509: /* (relative to the norms of the corresponding diagonal blocks) */
511: if (iend == nblks-2) {
512: d2 = PetscSqrtReal(exdnrm);
513: } else {
514: d2 = PetscSqrtReal(e[iwork[iend+1] + (iwork[iend+1] + (iend+1)*l2e)*l1e]);
515: }
517: /* this definition of TINY is analogous to the definition */
518: /* in the tridiagonal divide&conquer (dstedc) */
520: tiny = eps * PetscSqrtReal(e[iwork[iend] + (iwork[iend] + iend*l2e)*l1e])*d2;
521: if (e[(iwork[iend] + iend*l2e)*l1e] > tiny) {
523: /* no decoupling due to small norm of off-diagonal block */
525: ++iend;
526: goto L20;
527: }
528: }
529: }
531: /* ....(Sub) Problem determined: between diagonal blocks */
532: /* START and IEND. Compute its size and solve it.... */
534: nrblks = iend - start + 1;
535: if (nrblks == 1) {
537: /* Isolated problem is a single diagonal block */
539: nk = ksizes[start];
541: /* copy this isolated block into Z */
543: for (i = 0; i < nk; ++i) {
544: ip = np + i + 1;
545: for (j = 0; j <= i; ++j) z[ip + (np+j+1)*ldz] = d[i + (j + start*l2d)*l1d];
546: }
548: /* check whether there is enough workspace */
550: spneed = 2*nk*nk + nk * 6 + 1;
551: PetscCheck(spneed<=lwork,PETSC_COMM_SELF,PETSC_ERR_MEM,"dsbtdc: not enough workspace for DSYEVD, info = %" PetscBLASInt_FMT,lwork - 200 - spneed);
553: PetscCallBLAS("LAPACKsyevd",LAPACKsyevd_("V", "L", &nk,
554: &z[np + np*ldz], &ldz, &ev[np],
555: work, &lwork, &iwork[nblks-1], &liwork, info));
556: SlepcCheckLapackInfo("syevd",*info);
557: start = iend + 1;
558: np += nk;
560: /* go to the next irreducible subproblem */
562: goto L10;
563: }
565: /* ....Isolated problem consists of more than one diagonal block. */
566: /* Start the divide and conquer algorithm.... */
568: /* Scale: Divide by the maximum of all norms of diagonal blocks */
569: /* and singular values of the subdiagonal blocks */
571: /* ....determine maximum of the norms of all diagonal and subdiagonal */
572: /* blocks.... */
574: if (iend == nblks-1) anorm = exdnrm;
575: else anorm = e[iwork[iend] + (iwork[iend] + iend*l2e)*l1e];
576: for (k = start; k < iend; ++k) {
577: rp1 = iwork[k];
579: /* norm of diagonal block */
580: anorm = PetscMax(anorm,e[rp1 + (rp1 + k*l2e)*l1e]);
582: /* singular value of subdiagonal block */
583: anorm = PetscMax(anorm,e[(rp1 + k*l2e)*l1e]);
584: }
586: nk = 0;
587: for (k = start; k < iend+1; ++k) {
588: ksk = ksizes[k];
589: nk += ksk;
591: /* scale the diagonal block */
592: PetscCallBLAS("LAPACKlascl",LAPACKlascl_("L", &zero, &zero,
593: &anorm, &done, &ksk, &ksk, &d[k*l2d*l1d], &l1d, info));
594: SlepcCheckLapackInfo("lascl",*info);
596: /* scale the (approximated) off-diagonal block by dividing its */
597: /* singular values */
599: if (k != iend) {
601: /* the last subdiagonal block has index IEND-1 !!!! */
602: for (i = 0; i < iwork[k]; ++i) {
603: e[i + (iwork[k] + k*l2e)*l1e] /= anorm;
604: }
605: }
606: }
608: /* call the block-tridiagonal divide-and-conquer on the */
609: /* irreducible subproblem which has been identified */
611: PetscCall(BDC_dibtdc_(jobz, nk, nrblks, &ksizes[start], &d[start*l1d*l2d], l1d, l2d,
612: &e[start*l2e*l1e], &iwork[start], l1e, l2e, tau2, &ev[np],
613: &z[np + np*ldz], ldz, work, lwork, &iwork[nblks-1], liwork, info, 1));
614: PetscCheck(!*info,PETSC_COMM_SELF,PETSC_ERR_LIB,"dsbtdc: Error in DIBTDC, info = %" PetscBLASInt_FMT,*info);
616: /* ************************************************************************** */
618: /* Scale back the computed eigenvalues. */
620: PetscCallBLAS("LAPACKlascl",LAPACKlascl_("G", &zero, &zero, &done,
621: &anorm, &nk, &one, &ev[np], &nk, info));
622: SlepcCheckLapackInfo("lascl",*info);
624: start = iend + 1;
625: np += nk;
627: /* Go to the next irreducible subproblem. */
629: goto L10;
630: }
632: /* ....If the problem split any number of times, then the eigenvalues */
633: /* will not be properly ordered. Here we permute the eigenvalues */
634: /* (and the associated eigenvectors) across the irreducible parts */
635: /* into ascending order.... */
637: /* IF(NRBLKS.LT.NBLKS)THEN */
639: /* Use Selection Sort to minimize swaps of eigenvectors */
641: for (ii = 1; ii < n; ++ii) {
642: i = ii;
643: k = i;
644: p = ev[i];
645: for (j = ii; j < n; ++j) {
646: if (ev[j] < p) {
647: k = j;
648: p = ev[j];
649: }
650: }
651: if (k != i) {
652: ev[k] = ev[i];
653: ev[i] = p;
654: PetscCallBLAS("BLASswap",BLASswap_(&n, &z[i*ldz], &one, &z[k*ldz], &one));
655: }
656: }
658: /* ...Compute MINGAP (minimum difference between neighboring eigenvalue */
659: /* approximations).............................................. */
661: *mingap = ev[1] - ev[0];
662: PetscCheck(*mingap>=0.,PETSC_COMM_SELF,PETSC_ERR_LIB,"dsbtdc: Eigenvalue approximations are not ordered properly. Approximation 1 is larger than approximation 2.");
663: *mingapi = 1;
664: for (i = 2; i < n; ++i) {
665: absdiff = ev[i] - ev[i-1];
666: PetscCheck(absdiff>=0.,PETSC_COMM_SELF,PETSC_ERR_LIB,"dsbtdc: Eigenvalue approximations are not ordered properly. Approximation %" PetscBLASInt_FMT " is larger than approximation %" PetscBLASInt_FMT ".",i,i+1);
667: if (absdiff < *mingap) {
668: *mingap = absdiff;
669: *mingapi = i;
670: }
671: }
673: /* check whether the minimum gap between eigenvalue approximations */
674: /* may indicate severe inaccuracies in the eigenvector approximations */
676: if (*mingap <= tol / 10) *info = -103;
677: PetscFunctionReturn(PETSC_SUCCESS);
678: }