SUBROUTINE MVMGRC( TRANS, N, M, X, LDX, Y, LDY ) * .. * .. Scalar Arguments .. INTEGER LDY, LDX, M, N, TRANS * .. * .. Array Arguments .. DOUBLE PRECISION Y( LDY, * ), X( LDX, * ) * .. * * Purpose * ======= * * Compute * * Y(:,1:M) = op(A)*X(:,1:M) * * where op(A) is A or A' (the transpose of A). The A is the Grcar * matrix. * * Arguments * ========= * * TRANS (input) INTEGER * If TRANS = 0, compute Y(:,1:M) = A*X(:,1:M) * If TRANS = 1, compute Y(:,1:M) = A'*X(:,1:M) * * N (input) INTEGER * The order of the matrix A. N has to be an even number. * * M (input) INTEGERS * The number of columns of X to multiply. * * X (input) DOUBLE PRECISION array, dimension ( LDX, M ) * X contains the matrix (vectors) X. * * LDX (input) INTEGER * The leading dimension of array X, LDX >= max( 1, N ) * * Y (output) DOUBLE PRECISION array, dimension (LDY, M ) * contains the product of the matrix op(A) with X. * * LDY (input) INTEGER * The leading dimension of array Y, LDY >= max( 1, N ) * * =================================================================== * * .. Local Variables .. INTEGER I, K * IF ( TRANS.EQ.0 ) THEN * * Compute Y(:,1:M) = A*X(:,1:M) DO 20 K = 1,M Y( 1, K ) = X( 1, K ) + X( 2, K ) +X( 3, K ) + X( 4, K ) DO 10 I = 2,N-3 Y( I, K ) = -X( I-1, K ) + X( I, K ) + X( I+1, K ) \$ + X( I+2, K ) + X( I+3, K ) 10 CONTINUE Y( N-2, K ) = -X( N-3,k) + X( N-2, K ) + X( N-1, K ) \$ + X( N, K ) Y( N-1, K ) = -X( N-2,k) + X( N-1, K ) + X( N, K ) Y( N, K ) = -X( N-1,k) + X( N, K ) 20 CONTINUE * ELSE * * Compute Y(:,1:M) = A'*X(:,1:M) * DO 40 K = 1, M Y( 1, K ) = X( 1, K ) - X( 2, K ) Y( 2, K ) = X( 1, K ) + X( 2, K ) - X( 3, K ) Y( 3, K ) = X( 1, K ) + X( 2, K ) + X( 3, K ) - X( 4, K ) DO 30 I = 4, N-1 Y( I, K ) = X( I-3, K ) + X( I-2, K ) + X( I-1, K ) + \$ X( I, K ) - X( I+1, K ) 30 CONTINUE Y( N, K ) = X( N-3, K ) + X( N-2, K ) + X( N-1, K ) + \$ X( N, K ) 40 CONTINUE END IF * RETURN * * END OF MVMGRC END