#include "blaswrap.h"
#include "f2c.h"

/* Subroutine */ int dsbmv_(char *uplo, integer *n, integer *k, doublereal *
	alpha, doublereal *a, integer *lda, doublereal *x, integer *incx, 
	doublereal *beta, doublereal *y, integer *incy)
{
    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2, i__3, i__4;
    /* Local variables */
    static integer info;
    static doublereal temp1, temp2;
    static integer i__, j, l;
    extern logical lsame_(char *, char *);
    static integer kplus1, ix, iy, jx, jy, kx, ky;
    extern /* Subroutine */ int xerbla_(char *, integer *);
#define a_ref(a_1,a_2) a[(a_2)*a_dim1 + a_1]
/*  Purpose   
    =======   
    DSBMV  performs the matrix-vector  operation   
       y := alpha*A*x + beta*y,   
    where alpha and beta are scalars, x and y are n element vectors and   
    A is an n by n symmetric band matrix, with k super-diagonals.   
    Parameters   
    ==========   
    UPLO   - CHARACTER*1.   
             On entry, UPLO specifies whether the upper or lower   
             triangular part of the band matrix A is being supplied as   
             follows:   
                UPLO = 'U' or 'u'   The upper triangular part of A is   
                                    being supplied.   
                UPLO = 'L' or 'l'   The lower triangular part of A is   
                                    being supplied.   
             Unchanged on exit.   
    N      - INTEGER.   
             On entry, N specifies the order of the matrix A.   
             N must be at least zero.   
             Unchanged on exit.   
    K      - INTEGER.   
             On entry, K specifies the number of super-diagonals of the   
             matrix A. K must satisfy  0 .le. K.   
             Unchanged on exit.   
    ALPHA  - DOUBLE PRECISION.   
             On entry, ALPHA specifies the scalar alpha.   
             Unchanged on exit.   
    A      - DOUBLE PRECISION array of DIMENSION ( LDA, n ).   
             Before entry with UPLO = 'U' or 'u', the leading ( k + 1 )   
             by n part of the array A must contain the upper triangular   
             band part of the symmetric matrix, supplied column by   
             column, with the leading diagonal of the matrix in row   
             ( k + 1 ) of the array, the first super-diagonal starting at   
             position 2 in row k, and so on. The top left k by k triangle   
             of the array A is not referenced.   
             The following program segment will transfer the upper   
             triangular part of a symmetric band matrix from conventional   
             full matrix storage to band storage:   
                   DO 20, J = 1, N   
                      M = K + 1 - J   
                      DO 10, I = MAX( 1, J - K ), J   
                         A( M + I, J ) = matrix( I, J )   
                10    CONTINUE   
                20 CONTINUE   
             Before entry with UPLO = 'L' or 'l', the leading ( k + 1 )   
             by n part of the array A must contain the lower triangular   
             band part of the symmetric matrix, supplied column by   
             column, with the leading diagonal of the matrix in row 1 of   
             the array, the first sub-diagonal starting at position 1 in   
             row 2, and so on. The bottom right k by k triangle of the   
             array A is not referenced.   
             The following program segment will transfer the lower   
             triangular part of a symmetric band matrix from conventional   
             full matrix storage to band storage:   
                   DO 20, J = 1, N   
                      M = 1 - J   
                      DO 10, I = J, MIN( N, J + K )   
                         A( M + I, J ) = matrix( I, J )   
                10    CONTINUE   
                20 CONTINUE   
             Unchanged on exit.   
    LDA    - INTEGER.   
             On entry, LDA specifies the first dimension of A as declared   
             in the calling (sub) program. LDA must be at least   
             ( k + 1 ).   
             Unchanged on exit.   
    X      - DOUBLE PRECISION array of DIMENSION at least   
             ( 1 + ( n - 1 )*abs( INCX ) ).   
             Before entry, the incremented array X must contain the   
             vector x.   
             Unchanged on exit.   
    INCX   - INTEGER.   
             On entry, INCX specifies the increment for the elements of   
             X. INCX must not be zero.   
             Unchanged on exit.   
    BETA   - DOUBLE PRECISION.   
             On entry, BETA specifies the scalar beta.   
             Unchanged on exit.   
    Y      - DOUBLE PRECISION array of DIMENSION at least   
             ( 1 + ( n - 1 )*abs( INCY ) ).   
             Before entry, the incremented array Y must contain the   
             vector y. On exit, Y is overwritten by the updated vector y.   
    INCY   - INTEGER.   
             On entry, INCY specifies the increment for the elements of   
             Y. INCY must not be zero.   
             Unchanged on exit.   
    Level 2 Blas routine.   
    -- Written on 22-October-1986.   
       Jack Dongarra, Argonne National Lab.   
       Jeremy Du Croz, Nag Central Office.   
       Sven Hammarling, Nag Central Office.   
       Richard Hanson, Sandia National Labs.   
       Test the input parameters.   
       Parameter adjustments */
    a_dim1 = *lda;
    a_offset = 1 + a_dim1 * 1;
    a -= a_offset;
    --x;
    --y;
    /* Function Body */
    info = 0;
    if (! lsame_(uplo, "U") && ! lsame_(uplo, "L")) {
	info = 1;
    } else if (*n < 0) {
	info = 2;
    } else if (*k < 0) {
	info = 3;
    } else if (*lda < *k + 1) {
	info = 6;
    } else if (*incx == 0) {
	info = 8;
    } else if (*incy == 0) {
	info = 11;
    }
    if (info != 0) {
	xerbla_("DSBMV ", &info);
	return 0;
    }
/*     Quick return if possible. */
    if (*n == 0 || *alpha == 0. && *beta == 1.) {
	return 0;
    }
/*     Set up the start points in  X  and  Y. */
    if (*incx > 0) {
	kx = 1;
    } else {
	kx = 1 - (*n - 1) * *incx;
    }
    if (*incy > 0) {
	ky = 1;
    } else {
	ky = 1 - (*n - 1) * *incy;
    }
/*     Start the operations. In this version the elements of the array A   
       are accessed sequentially with one pass through A.   
       First form  y := beta*y. */
    if (*beta != 1.) {
	if (*incy == 1) {
	    if (*beta == 0.) {
		i__1 = *n;
		for (i__ = 1; i__ <= i__1; ++i__) {
		    y[i__] = 0.;
/* L10: */
		}
	    } else {
		i__1 = *n;
		for (i__ = 1; i__ <= i__1; ++i__) {
		    y[i__] = *beta * y[i__];
/* L20: */
		}
	    }
	} else {
	    iy = ky;
	    if (*beta == 0.) {
		i__1 = *n;
		for (i__ = 1; i__ <= i__1; ++i__) {
		    y[iy] = 0.;
		    iy += *incy;
/* L30: */
		}
	    } else {
		i__1 = *n;
		for (i__ = 1; i__ <= i__1; ++i__) {
		    y[iy] = *beta * y[iy];
		    iy += *incy;
/* L40: */
		}
	    }
	}
    }
    if (*alpha == 0.) {
	return 0;
    }
    if (lsame_(uplo, "U")) {
/*        Form  y  when upper triangle of A is stored. */
	kplus1 = *k + 1;
	if (*incx == 1 && *incy == 1) {
	    i__1 = *n;
	    for (j = 1; j <= i__1; ++j) {
		temp1 = *alpha * x[j];
		temp2 = 0.;
		l = kplus1 - j;
/* Computing MAX */
		i__2 = 1, i__3 = j - *k;
		i__4 = j - 1;
		for (i__ = max(i__2,i__3); i__ <= i__4; ++i__) {
		    y[i__] += temp1 * a_ref(l + i__, j);
		    temp2 += a_ref(l + i__, j) * x[i__];
/* L50: */
		}
		y[j] = y[j] + temp1 * a_ref(kplus1, j) + *alpha * temp2;
/* L60: */
	    }
	} else {
	    jx = kx;
	    jy = ky;
	    i__1 = *n;
	    for (j = 1; j <= i__1; ++j) {
		temp1 = *alpha * x[jx];
		temp2 = 0.;
		ix = kx;
		iy = ky;
		l = kplus1 - j;
/* Computing MAX */
		i__4 = 1, i__2 = j - *k;
		i__3 = j - 1;
		for (i__ = max(i__4,i__2); i__ <= i__3; ++i__) {
		    y[iy] += temp1 * a_ref(l + i__, j);
		    temp2 += a_ref(l + i__, j) * x[ix];
		    ix += *incx;
		    iy += *incy;
/* L70: */
		}
		y[jy] = y[jy] + temp1 * a_ref(kplus1, j) + *alpha * temp2;
		jx += *incx;
		jy += *incy;
		if (j > *k) {
		    kx += *incx;
		    ky += *incy;
		}
/* L80: */
	    }
	}
    } else {
/*        Form  y  when lower triangle of A is stored. */
	if (*incx == 1 && *incy == 1) {
	    i__1 = *n;
	    for (j = 1; j <= i__1; ++j) {
		temp1 = *alpha * x[j];
		temp2 = 0.;
		y[j] += temp1 * a_ref(1, j);
		l = 1 - j;
/* Computing MIN */
		i__4 = *n, i__2 = j + *k;
		i__3 = min(i__4,i__2);
		for (i__ = j + 1; i__ <= i__3; ++i__) {
		    y[i__] += temp1 * a_ref(l + i__, j);
		    temp2 += a_ref(l + i__, j) * x[i__];
/* L90: */
		}
		y[j] += *alpha * temp2;
/* L100: */
	    }
	} else {
	    jx = kx;
	    jy = ky;
	    i__1 = *n;
	    for (j = 1; j <= i__1; ++j) {
		temp1 = *alpha * x[jx];
		temp2 = 0.;
		y[jy] += temp1 * a_ref(1, j);
		l = 1 - j;
		ix = jx;
		iy = jy;
/* Computing MIN */
		i__4 = *n, i__2 = j + *k;
		i__3 = min(i__4,i__2);
		for (i__ = j + 1; i__ <= i__3; ++i__) {
		    ix += *incx;
		    iy += *incy;
		    y[iy] += temp1 * a_ref(l + i__, j);
		    temp2 += a_ref(l + i__, j) * x[ix];
/* L110: */
		}
		y[jy] += *alpha * temp2;
		jx += *incx;
		jy += *incy;
/* L120: */
	    }
	}
    }
    return 0;
/*     End of DSBMV . */
} /* dsbmv_ */
#undef a_ref

