def linear (x, parameters):
    """Sigmoid function
    POI = a + (b * x )
    
    Parameters
    ----------
    x: float or array of floats
        variable
    parameters: dict
        dictionary containing 'linear_a', and 'linear_b'
        
    Returns
    -------
    float or array of floats:
        function  result
    """
    a = parameters['linear_a']
    b = parameters['linear_b']
    return a + (b * x)