def parse_stiff_dict(element):
    """Parse stiffness dictionary 

    Args : 
        element (dict) : element dictionary defined in configuration file 
    
    Return : 
        start_node (int)
        end_node (int)
        stiffness (int or float) 

    Variables : 
        E (int or float) : elasticity 
        A (int or float) : area
        L (int or float) : length
    """
    
    start_node = element.get('start_node', None)
    end_node = element.get('end_node', None)
    stiffness = element.get('stiffness', None)
    E = element.get('E', None)
    A = element.get('A', None)
    L = element.get('L', None)

    print(E, A, L )

    if start_node and end_node : 
        # the node notation starts from 1 
        start_node -= 1
        end_node -= 1

    if not stiffness : 
        # suppose the element is truss element
        stiffness = E*A/L

    return start_node, end_node, stiffness