Function dgbmv

For general band matrix A and vector X and Y compute Y = alpha * A * X + beta * Y or Y = alpha * A.T * X + beta * Y

(transA string, M int, N int, KL int, KU int,
    alpha float64, A []float64, lda int,
    X []float64, incX int, beta float64,
    Y []float64, incY int)