LAPACK
3.4.2
LAPACK: Linear Algebra PACKage

Go to the source code of this file.
Functions/Subroutines  
subroutine  clalsd (UPLO, SMLSIZ, N, NRHS, D, E, B, LDB, RCOND, RANK, WORK, RWORK, IWORK, INFO) 
CLALSD uses the singular value decomposition of A to solve the least squares problem. 
subroutine clalsd  (  character  UPLO, 
integer  SMLSIZ,  
integer  N,  
integer  NRHS,  
real, dimension( * )  D,  
real, dimension( * )  E,  
complex, dimension( ldb, * )  B,  
integer  LDB,  
real  RCOND,  
integer  RANK,  
complex, dimension( * )  WORK,  
real, dimension( * )  RWORK,  
integer, dimension( * )  IWORK,  
integer  INFO  
) 
CLALSD uses the singular value decomposition of A to solve the least squares problem.
Download CLALSD + dependencies [TGZ] [ZIP] [TXT]CLALSD uses the singular value decomposition of A to solve the least squares problem of finding X to minimize the Euclidean norm of each column of A*XB, where A is NbyN upper bidiagonal, and X and B are NbyNRHS. The solution X overwrites B. The singular values of A smaller than RCOND times the largest singular value are treated as zero in solving the least squares problem; in this case a minimum norm solution is returned. The actual singular values are returned in D in ascending order. This code makes very mild assumptions about floating point arithmetic. It will work on machines with a guard digit in add/subtract, or on those binary machines without guard digits which subtract like the Cray XMP, Cray YMP, Cray C 90, or Cray 2. It could conceivably fail on hexadecimal or decimal machines without guard digits, but we know of none.
[in]  UPLO  UPLO is CHARACTER*1 = 'U': D and E define an upper bidiagonal matrix. = 'L': D and E define a lower bidiagonal matrix. 
[in]  SMLSIZ  SMLSIZ is INTEGER The maximum size of the subproblems at the bottom of the computation tree. 
[in]  N  N is INTEGER The dimension of the bidiagonal matrix. N >= 0. 
[in]  NRHS  NRHS is INTEGER The number of columns of B. NRHS must be at least 1. 
[in,out]  D  D is REAL array, dimension (N) On entry D contains the main diagonal of the bidiagonal matrix. On exit, if INFO = 0, D contains its singular values. 
[in,out]  E  E is REAL array, dimension (N1) Contains the superdiagonal entries of the bidiagonal matrix. On exit, E has been destroyed. 
[in,out]  B  B is COMPLEX array, dimension (LDB,NRHS) On input, B contains the right hand sides of the least squares problem. On output, B contains the solution X. 
[in]  LDB  LDB is INTEGER The leading dimension of B in the calling subprogram. LDB must be at least max(1,N). 
[in]  RCOND  RCOND is REAL The singular values of A less than or equal to RCOND times the largest singular value are treated as zero in solving the least squares problem. If RCOND is negative, machine precision is used instead. For example, if diag(S)*X=B were the least squares problem, where diag(S) is a diagonal matrix of singular values, the solution would be X(i) = B(i) / S(i) if S(i) is greater than RCOND*max(S), and X(i) = 0 if S(i) is less than or equal to RCOND*max(S). 
[out]  RANK  RANK is INTEGER The number of singular values of A greater than RCOND times the largest singular value. 
[out]  WORK  WORK is COMPLEX array, dimension (N * NRHS). 
[out]  RWORK  RWORK is REAL array, dimension at least (9*N + 2*N*SMLSIZ + 8*N*NLVL + 3*SMLSIZ*NRHS + MAX( (SMLSIZ+1)**2, N*(1+NRHS) + 2*NRHS ), where NLVL = MAX( 0, INT( LOG_2( MIN( M,N )/(SMLSIZ+1) ) ) + 1 ) 
[out]  IWORK  IWORK is INTEGER array, dimension (3*N*NLVL + 11*N). 
[out]  INFO  INFO is INTEGER = 0: successful exit. < 0: if INFO = i, the ith argument had an illegal value. > 0: The algorithm failed to compute a singular value while working on the submatrix lying in rows and columns INFO/(N+1) through MOD(INFO,N+1). 
Definition at line 186 of file clalsd.f.