def mtx_refl(nv, reps=1):
    import numpy as np
    from scipy import linalg as spla
    from ..const import PRM
    if spla.norm(nv) < PRM.ZERO_VEC_TOL:
        raise ValueError("Norm of 'nv' is too small.")
    nv = make_nd_vec(nv, nd=3, t=np.float64, norm=True)
    if not np.isscalar(reps):
        raise ValueError("'reps' must be scalar.")
    if not np.issubdtype(type(reps), int):
        raise ValueError("'reps' must be an integer.")
    if not reps > 0:
        raise ValueError("'reps' must be a positive integer.")
    base_mtx = np.zeros(shape=(3,3), dtype=np.float64)
    for i in range(3):
        for j in range(i,3):
            if i==j:
                base_mtx[i,j] = 1 - 2*nv[i]**2
            else:
                base_mtx[i,j] = base_mtx[j,i] = -2*nv[i]*nv[j]
    refl_mtx= spla.block_diag(*[base_mtx for i in range(reps)])
    return refl_mtx