ex_A.m :  UL factorization
ex_B.m :  LU with partial pivoting
ex_C.m :  Back substitution in a ref matrix
ex_D.m :  return coefficients of Lagrange interpolating polynomial
ex_E.m :  romberg integration
ex_F.m :  Least squares
ex_G.m :  trapezoid rule
ex_H.m :  simpson's rule
ex_I.m :  fmin by golden ratio
ex_J.m :  power method for dominate eigenvalue