def _coeff_isneg(a):
    """Return True if the leading Number is negative.

    Examples
    ========

    >>> from sympy.core.function import _coeff_isneg
    >>> from sympy import S, Symbol, oo, pi
    >>> _coeff_isneg(-3*pi)
    True
    >>> _coeff_isneg(S(3))
    False
    >>> _coeff_isneg(-oo)
    True
    >>> _coeff_isneg(Symbol('n', negative=True)) # coeff is 1
    False

    For matrix expressions:

    >>> from sympy import MatrixSymbol, sqrt
    >>> A = MatrixSymbol("A", 3, 3)
    >>> _coeff_isneg(-sqrt(2)*A)
    True
    >>> _coeff_isneg(sqrt(2)*A)
    False
    """
    if a.is_MatMul:
        a = a.args[0]
    if a.is_Mul:
        a = a.args[0]
    return a.is_Number and a.is_extended_negative
