# sorcsd2by1.f - Man Page

## Synopsis

### Functions/Subroutines

subroutine **sorcsd2by1** (JOBU1, JOBU2, JOBV1T, M, P, Q, X11, LDX11, X21, LDX21, THETA, U1, LDU1, U2, LDU2, V1T, LDV1T, WORK, LWORK, IWORK, INFO)**SORCSD2BY1**

## Function/Subroutine Documentation

### subroutine sorcsd2by1 (character JOBU1, character JOBU2, character JOBV1T, integer M, integer P, integer Q, real, dimension(ldx11,*) X11, integer LDX11, real, dimension(ldx21,*) X21, integer LDX21, real, dimension(*) THETA, real, dimension(ldu1,*) U1, integer LDU1, real, dimension(ldu2,*) U2, integer LDU2, real, dimension(ldv1t,*) V1T, integer LDV1T, real, dimension(*) WORK, integer LWORK, integer, dimension(*) IWORK, integer INFO)

**SORCSD2BY1**

**Purpose:**

SORCSD2BY1 computes the CS decomposition of an M-by-Q matrix X with orthonormal columns that has been partitioned into a 2-by-1 block structure: [ I1 0 0 ] [ 0 C 0 ] [ X11 ] [ U1 | ] [ 0 0 0 ] X = [-----] = [---------] [----------] V1**T . [ X21 ] [ | U2 ] [ 0 0 0 ] [ 0 S 0 ] [ 0 0 I2] X11 is P-by-Q. The orthogonal matrices U1, U2, and V1 are P-by-P, (M-P)-by-(M-P), and Q-by-Q, respectively. C and S are R-by-R nonnegative diagonal matrices satisfying C^2 + S^2 = I, in which R = MIN(P,M-P,Q,M-Q). I1 is a K1-by-K1 identity matrix and I2 is a K2-by-K2 identity matrix, where K1 = MAX(Q+P-M,0), K2 = MAX(Q-P,0).

**Parameters:***JOBU1*JOBU1 is CHARACTER = 'Y': U1 is computed; otherwise: U1 is not computed.

*JOBU2*JOBU2 is CHARACTER = 'Y': U2 is computed; otherwise: U2 is not computed.

*JOBV1T*JOBV1T is CHARACTER = 'Y': V1T is computed; otherwise: V1T is not computed.

*M*M is INTEGER The number of rows in X.

*P*P is INTEGER The number of rows in X11. 0 <= P <= M.

*Q*Q is INTEGER The number of columns in X11 and X21. 0 <= Q <= M.

*X11*X11 is REAL array, dimension (LDX11,Q) On entry, part of the orthogonal matrix whose CSD is desired.

*LDX11*LDX11 is INTEGER The leading dimension of X11. LDX11 >= MAX(1,P).

*X21*X21 is REAL array, dimension (LDX21,Q) On entry, part of the orthogonal matrix whose CSD is desired.

*LDX21*LDX21 is INTEGER The leading dimension of X21. LDX21 >= MAX(1,M-P).

*THETA*THETA is REAL array, dimension (R), in which R = MIN(P,M-P,Q,M-Q). C = DIAG( COS(THETA(1)), ... , COS(THETA(R)) ) and S = DIAG( SIN(THETA(1)), ... , SIN(THETA(R)) ).

*U1*U1 is REAL array, dimension (P) If JOBU1 = 'Y', U1 contains the P-by-P orthogonal matrix U1.

*LDU1*LDU1 is INTEGER The leading dimension of U1. If JOBU1 = 'Y', LDU1 >= MAX(1,P).

*U2*U2 is REAL array, dimension (M-P) If JOBU2 = 'Y', U2 contains the (M-P)-by-(M-P) orthogonal matrix U2.

*LDU2*LDU2 is INTEGER The leading dimension of U2. If JOBU2 = 'Y', LDU2 >= MAX(1,M-P).

*V1T*V1T is REAL array, dimension (Q) If JOBV1T = 'Y', V1T contains the Q-by-Q matrix orthogonal matrix V1**T.

*LDV1T*LDV1T is INTEGER The leading dimension of V1T. If JOBV1T = 'Y', LDV1T >= MAX(1,Q).

*WORK*WORK is REAL array, dimension (MAX(1,LWORK)) On exit, if INFO = 0, WORK(1) returns the optimal LWORK. If INFO > 0 on exit, WORK(2:R) contains the values PHI(1), ..., PHI(R-1) that, together with THETA(1), ..., THETA(R), define the matrix in intermediate bidiagonal-block form remaining after nonconvergence. INFO specifies the number of nonzero PHI's.

*LWORK*LWORK is INTEGER The dimension of the array WORK. If LWORK = -1, then a workspace query is assumed; the routine only calculates the optimal size of the WORK array, returns this value as the first entry of the work array, and no error message related to LWORK is issued by XERBLA.

*IWORK*IWORK is INTEGER array, dimension (M-MIN(P,M-P,Q,M-Q))

*INFO*INFO is INTEGER = 0: successful exit. < 0: if INFO = -i, the i-th argument had an illegal value. > 0: SBBCSD did not converge. See the description of WORK above for details.

**References:**

[1] Brian D. Sutton. Computing the complete CS decomposition. Numer. Algorithms, 50(1):33-65, 2009.

**Author:**Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

**Date:**July 2012

Definition at line 235 of file sorcsd2by1.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page sorcsd2by1(3) is an alias of sorcsd2by1.f(3).

Tue Nov 14 2017 Version 3.8.0 LAPACK