z_cg z_cg_r z_cr z_cr_r

z_cg_r() void z_cg_r ( int  n, const doublecomplex  b[], doublecomplex  x[], int  maxiter, int *  iter, double *  res, int  lwork, doublecomplex  work[], int *  info, doublecomplex  xx[], doublecomplex  yy[], int *  irev  ) Solution of linear system Ax = b using conjugate gradient (CG) method (Hermitian positive definite matrices) (Reverse communication version) Purpose This routine solves the linear system Ax = b with Hermitian positive definite coefficient matrix using the conjugate gradient (CG) method with preconditioning. Parameters [in] n Dimension of the matrix. (n >= 0) (if n = 0, returns without computation) [in] b[] Array b[lb] (lb >= n) Right hand side vector b. [in,out] x[] Array x[lx] (lx >= n) [in] Initial guess of solution. [out] Obtained approximate solution. [in] maxiter Maximum number of iterations. (maxiter > 0) [out] iter Final number of iterations. [out] res Final residual norm norm(b - A*x). [in] lwork Size of array work[]. (lwork >= 3*n) [out] work[] Array work[lwork] Work array. [out] info = 0: Successful exit. < 0: The (-info)-th argument is invalid. = 1: (Warning) Matrix A is not positive definite (computation continued). = 2: (Warning) Preconditioner matrix M is not positive definite (computation continued). = 11: Maximum number of iterations exceeded. = 12: Matrix A is singular. [in,out] xx[] Array xx[] for matvec and psolve operations. [in,out] yy[] Array yy[] for matvec and psolve operations. [in,out] irev Control variable for reverse communication. [in] Before first call, irev should be initialized to zero. On succeeding calls, irev should not be altered (except if converged). [out] If irev is not zero, complete the following process and call this routine again. = 0: Computation finished. See return code in info. = 1, 2: matvec operation. User should set A*xx in yy[]. Do not alter any other variables. = 21: psolve operation. User should set solution of M*xx = yy in xx[]. Do not alter any other variables. = 91, 92: Returned on every iteration for the convergence test. Set irev = 99 if converged. Do not alter irev otherwise. The latest values in x[], iter and res can be used to decide the convergence. Further, these values may be used to output the intermediate results.