1. “Conjugate gradient methods for partial differential equations,”;Chandra,1978
2. “The modified conjugate residual method for partial differential equations,”;Chandra,1977
3. “A generalized conjugate gradient method for nonsymmetric systems of linear equations,”;Concus,1976
4. “A generalized conjugate gradient method for the numerical solution of elliptic partial differential equations,”;Concus,1976
5. Dongarra, J.J., Leaf, G.K., and Minkoff, M. (1981). “A preconditioned conjugate gradient method for solving a class of non-symmetric linear systems,” Argonne Nat. Lab. Rep. ANL-81-71.