功能：用拉格朗日方法求解等式约束二次规划：min f(x)=0.5*x Hx+c x,s.t.Ax=b

输入：H,c分别是目标函数的矩阵和向量，A,b分别是约束条件中的矩阵和向量

输出：（x,lam)是KT点，fval是最优值。-Function: Lagrangian method for solving equality constrained quadratic programming: min f (x) = 0.5* x Hx+ c x, s.t.Ax = b

Input: H, c are the matrix and vector objective function, A, b are the constraints in the matrices and vectors

Output: (x, lam) is KT point, fval optimal value.