preconjgrad：预处理共轭梯度法求线性方程组Ax=b的解

conjgrad：共轭梯度法求线性方程组Ax=b的解

twostep:两部迭代法求线性方程组Ax=b的解

fastdown:快速下降法求线性方程组Ax=b的解-preconjgrad: preconditioned conjugate gradient method for solving linear equations Ax = b solution conjgrad: conjugate gradient method for solving linear equations Ax = b solution twostep: Two iterative methods for solving linear equations Ax = b, Solution fastdown: rapid descent method for solving linear equations Ax = b solution