def DotProduct(v,w):
        return v*w
    
    def SqLength(v):
        return v*v
    
    def Length(v):
        return sqrt( v.SqLength() )
    
    def Normalize(v,length=1.0):
        w=Vector()
        if (v.Length()>0.0):
            w=v*(1.0/v.Length())
    
    def Hat2(v):
        return Vector([ -v[1],v[0] ])

    def Projection(v,e):
        return e*(v*e)/e.SqLength()
    
    def Complement(v,e):
        return v-v.Projection(e)