Use python to calculate the N smallest eigenvalues of a tridiagonal matrix，,## module ei

Use python to calculate the N smallest eigenvalues of a tridiagonal matrix，,## module ei

## module eigenvals3''' lam = eigenvals3(d,c,N).    Returns the N smallest eigenvalues of a    tridiagonal matrix [A] = [c\d\c].'''    from lamRange import *from ridder import *from sturmSeq import sturmSeqfrom numpy import zerosdef eigenvals3(d,c,N):    def f(x):             # f(x) = |[A] - x[I]|        p = sturmSeq(d,c,x)        return p[len(p)-1]    lam = zeros(N)    r = lamRange(d,c,N)   # Bracket eigenvalues    for i in range(N):    # Solve by Brent's method        lam[i] = ridder(f,r[i],r[i+1])    return lam