HSL_MA79 is a mixed precision sparse symmetric solver for solving one or more linear systems . A factorization of using single precision (that is, 32-bit real arithmetic) is performed using a direct solver (MA57 or HSL_MA77) and then reﬁnement (iterative reﬁnement and, in some cases, FGMRES) in double precision (that is, 64-bit real arithmetic) is used to recover higher accuracy. This technique is termed a mixed precision approach. If reﬁnement fails to achieve the requested accuracy, a double precision factorization is performed.
Use of single precision arithmetic substantially reduces the amount of data that is moved around within a sparse direct solver, and on a number of modern architectures, it is currently signiﬁcantly faster than double precision computation. Thus HSL_MA79 oﬀers the potential of obtaining a solution to to double-precision accuracy more rapidly than using a direct solver in double precision. HSL_MA79 is primarily designed for solving very large systems.