Add magnitude function

[lizliz]

Add the magnitude function for a given input distance matrix $D$. This is related to Sara Kalisnik's work, one example of which is here: https://www.sciencedirect.com/science/article/pii/S0022404923000798

A starting point for the code is below.

def MagnitudeFunction(D,t_range = [.1,10], t_n = 100):
    T = np.linspace(t_range[0],t_range[1],t_n)
    M = []
    for t in T:
        tZ = np.exp(-t*D)
        tZinv = inv(tZ)
        m = np.sum(tZinv)
        M.append(m)
    return T,M

T,M = MagnitudeFunction(D, t_range = [.1,100])
plt.plot(T,M)