.TH "cgeqr.f" 3 "Wed May 24 2017" "Version 3.7.0" "LAPACK" \" -*- nroff -*-
.ad l
.nh
.SH NAME
cgeqr.f
.SH SYNOPSIS
.br
.PP
.SS "Functions/Subroutines"

.in +1c
.ti -1c
.RI "subroutine \fBcgeqr\fP (M, \fBN\fP, A, \fBLDA\fP, T, TSIZE, WORK, LWORK, INFO)"
.br
.in -1c
.SH "Function/Subroutine Documentation"
.PP 
.SS "subroutine cgeqr (integer M, integer N, complex, dimension( lda, * ) A, integer LDA, complex, dimension( * ) T, integer TSIZE, complex, dimension( * ) WORK, integer LWORK, integer INFO)"

.PP
\fBPurpose:\fP
.RS 4
CGEQR computes a QR factorization of an M-by-N matrix A\&.  
.RE
.PP
\fBParameters:\fP
.RS 4
\fIM\fP 
.PP
.nf
          M is INTEGER
          The number of rows of the matrix A.  M >= 0.
.fi
.PP
.br
\fIN\fP 
.PP
.nf
          N is INTEGER
          The number of columns of the matrix A.  N >= 0.
.fi
.PP
.br
\fIA\fP 
.PP
.nf
          A is COMPLEX array, dimension (LDA,N)
          On entry, the M-by-N matrix A.
          On exit, the elements on and above the diagonal of the array
          contain the min(M,N)-by-N upper trapezoidal matrix R
          (R is upper triangular if M >= N);
          the elements below the diagonal are used to store part of the 
          data structure to represent Q.
.fi
.PP
.br
\fILDA\fP 
.PP
.nf
          LDA is INTEGER
          The leading dimension of the array A.  LDA >= max(1,M).
.fi
.PP
.br
\fIT\fP 
.PP
.nf
          T is COMPLEX array, dimension (MAX(5,TSIZE))
          On exit, if INFO = 0, T(1) returns optimal (or either minimal 
          or optimal, if query is assumed) TSIZE. See TSIZE for details.
          Remaining T contains part of the data structure used to represent Q.
          If one wants to apply or construct Q, then one needs to keep T 
          (in addition to A) and pass it to further subroutines.
.fi
.PP
.br
\fITSIZE\fP 
.PP
.nf
          TSIZE is INTEGER
          If TSIZE >= 5, the dimension of the array T.
          If TSIZE = -1 or -2, then a workspace query is assumed. The routine
          only calculates the sizes of the T and WORK arrays, returns these
          values as the first entries of the T and WORK arrays, and no error
          message related to T or WORK is issued by XERBLA.
          If TSIZE = -1, the routine calculates optimal size of T for the 
          optimum performance and returns this value in T(1).
          If TSIZE = -2, the routine calculates minimal size of T and 
          returns this value in T(1).
.fi
.PP
.br
\fIWORK\fP 
.PP
.nf
          (workspace) COMPLEX array, dimension (MAX(1,LWORK))
          On exit, if INFO = 0, WORK(1) contains optimal (or either minimal
          or optimal, if query was assumed) LWORK.
          See LWORK for details.
.fi
.PP
.br
\fILWORK\fP 
.PP
.nf
          LWORK is INTEGER
          The dimension of the array WORK.
          If LWORK = -1 or -2, then a workspace query is assumed. The routine
          only calculates the sizes of the T and WORK arrays, returns these
          values as the first entries of the T and WORK arrays, and no error
          message related to T or WORK is issued by XERBLA.
          If LWORK = -1, the routine calculates optimal size of WORK for the
          optimal performance and returns this value in WORK(1).
          If LWORK = -2, the routine calculates minimal size of WORK and 
          returns this value in WORK(1).
.fi
.PP
.br
\fIINFO\fP 
.PP
.nf
          INFO is INTEGER
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value
.fi
.PP
 
.RE
.PP
\fBAuthor:\fP
.RS 4
Univ\&. of Tennessee 
.PP
Univ\&. of California Berkeley 
.PP
Univ\&. of Colorado Denver 
.PP
NAG Ltd\&. 
.RE
.PP
\fBFurther Details\fP
.RS 4

.RE
.PP
The goal of the interface is to give maximum freedom to the developers for creating any QR factorization algorithm they wish\&. The triangular (trapezoidal) R has to be stored in the upper part of A\&. The lower part of A and the array T can be used to store any relevant information for applying or constructing the Q factor\&. The WORK array can safely be discarded after exit\&.
.PP
Caution: One should not expect the sizes of T and WORK to be the same from one LAPACK implementation to the other, or even from one execution to the other\&. A workspace query (for T and WORK) is needed at each execution\&. However, for a given execution, the size of T and WORK are fixed and will not change from one query to the next\&.
.PP
\fBFurther Details particular to this LAPACK implementation:\fP
.RS 4

.RE
.PP
These details are particular for this LAPACK implementation\&. Users should not take them for granted\&. These details may change in the future, and are unlikely not true for another LAPACK implementation\&. These details are relevant if one wants to try to understand the code\&. They are not part of the interface\&.
.PP
In this version,
.PP
T(2): row block size (MB) T(3): column block size (NB) T(6:TSIZE): data structure needed for Q, computed by CLATSQR or CGEQRT
.PP
Depending on the matrix dimensions M and N, and row and column block sizes MB and NB returned by ILAENV, CGEQR will use either CLATSQR (if the matrix is tall-and-skinny) or CGEQRT to compute the QR factorization\&.
.SH "Author"
.PP 
Generated automatically by Doxygen for LAPACK from the source code\&.