Interpolate a y = f(x) function using linear interpolation.

    Rigid means the x_new_axis has to be in x_axis's range.

def rigid_linear_interpolate(x_axis, y_axis, x_new_axis):
    """Interpolate a y = f(x) function using linear interpolation.

    Rigid means the x_new_axis has to be in x_axis's range.
    """
    f = interp1d(x_axis, y_axis)
    return f(x_new_axis)