SUBROUTINE SLARGE( N, A, LDA, ISEED, WORK, INFO ) * * -- LAPACK auxiliary test routine (version 3.1) * Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. * November 2006 * * .. Scalar Arguments .. INTEGER INFO, LDA, N * .. * .. Array Arguments .. INTEGER ISEED( 4 ) REAL A( LDA, * ), WORK( * ) * .. * * Purpose * ======= * * SLARGE pre- and post-multiplies a real general n by n matrix A * with a random orthogonal matrix: A = U*D*U'. * * Arguments * ========= * * N (input) INTEGER * The order of the matrix A. N >= 0. * * A (input/output) REAL array, dimension (LDA,N) * On entry, the original n by n matrix A. * On exit, A is overwritten by U*A*U' for some random * orthogonal matrix U. * * LDA (input) INTEGER * The leading dimension of the array A. LDA >= N. * * ISEED (input/output) INTEGER array, dimension (4) * On entry, the seed of the random number generator; the array * elements must be between 0 and 4095, and ISEED(4) must be * odd. * On exit, the seed is updated. * * WORK (workspace) REAL array, dimension (2*N) * * INFO (output) INTEGER * = 0: successful exit * < 0: if INFO = -i, the i-th argument had an illegal value * * ===================================================================== * * .. Parameters .. REAL ZERO, ONE PARAMETER ( ZERO = 0.0E+0, ONE = 1.0E+0 ) * .. * .. Local Scalars .. INTEGER I REAL TAU, WA, WB, WN * .. * .. External Subroutines .. EXTERNAL SGEMV, SGER, SLARNV, SSCAL, XERBLA * .. * .. Intrinsic Functions .. INTRINSIC MAX, SIGN * .. * .. External Functions .. REAL SNRM2 EXTERNAL SNRM2 * .. * .. Executable Statements .. * * Test the input arguments * INFO = 0 IF( N.LT.0 ) THEN INFO = -1 ELSE IF( LDA.LT.MAX( 1, N ) ) THEN INFO = -3 END IF IF( INFO.LT.0 ) THEN CALL XERBLA( 'SLARGE', -INFO ) RETURN END IF * * pre- and post-multiply A by random orthogonal matrix * DO 10 I = N, 1, -1 * * generate random reflection * CALL SLARNV( 3, ISEED, N-I+1, WORK ) WN = SNRM2( N-I+1, WORK, 1 ) WA = SIGN( WN, WORK( 1 ) ) IF( WN.EQ.ZERO ) THEN TAU = ZERO ELSE WB = WORK( 1 ) + WA CALL SSCAL( N-I, ONE / WB, WORK( 2 ), 1 ) WORK( 1 ) = ONE TAU = WB / WA END IF * * multiply A(i:n,1:n) by random reflection from the left * CALL SGEMV( 'Transpose', N-I+1, N, ONE, A( I, 1 ), LDA, WORK, \$ 1, ZERO, WORK( N+1 ), 1 ) CALL SGER( N-I+1, N, -TAU, WORK, 1, WORK( N+1 ), 1, A( I, 1 ), \$ LDA ) * * multiply A(1:n,i:n) by random reflection from the right * CALL SGEMV( 'No transpose', N, N-I+1, ONE, A( 1, I ), LDA, \$ WORK, 1, ZERO, WORK( N+1 ), 1 ) CALL SGER( N, N-I+1, -TAU, WORK( N+1 ), 1, WORK, 1, A( 1, I ), \$ LDA ) 10 CONTINUE RETURN * * End of SLARGE * END