Most routines in LAPACK occur in four versions: REAL, DOUBLE PRECISION, COMPLEX, and COMPLEX*16. The first three versions (REAL, DOUBLE PRECISION, and COMPLEX) are written in standard Fortran 77 and are completely portable; the COMPLEX*16 version is provided for those compilers which allow this data type. For convenience, we often refer to routines by their single precision names; the leading `S' can be replaced by a `D' for double precision, a `C' for complex, or a `Z' for complex*16. For LAPACK use and testing you must decide which version(s) of the package you intend to install at your site (for example, REAL and COMPLEX on a Cray computer or DOUBLE PRECISION and COMPLEX*16 on an IBM computer).