Help Files: Fortran77: NAG Library

     HELP                      Sep. 15, 1984               F77/NAG_LIB



          NAG Library of Mathematical and Statistical Procedures

     The NAG library, which includes about 500 Fortran  callable  sub-
     routines,  is  available for VAX UNIX.  There are both single and
     double precision versions; check with your  system  administrator
     to  see  if  your  system  has the NAG library, how to access it.
     Your administrator can also tell you where the  documentation  (6
     volumes)  is  kept.   The rest of this write-up discusses assumes
     you have the double precision version.

     While NAG includes mainly mathematical and statistical  routines,
     the  library  also  includes  sorting routines in chapter M01 and
     machine and mathematical constant routines in chapter X.  To  use
     the double precision version, specify '-lnagd' to f77:

             f77 prog.f -lnagd

     If the NAG library does not include a subroutine for what you are
     doing,  see  "help  f77  libraries"  for information on other li-
     braries.

     The NAG manual is written to be applicable  to  both  single  and
     double  precision  versions  of  the library.  Generally you will
     have to supply double precision arguments.  Where the  documenta-
     tion  indicates  "real" in italics, use 'double precision' on VAX
     UNIX.  If you have written your program in single precision,  see
     "help f77 to_double" to see what changes are needed to use double
     precision.

     There are five common errors in using NAG routines:


     1.   Using single precision when double precision is required.


     2.   Not checking the error flag.  Most routines  have  an  error
          flag  that  NAG  sets  to an error value when something goes
          wrong; it is your responsibility to check it.


     3.   Omitting arguments.  NAG routines often have many  arguments
          that are required even if you don't use the result.


     4.   Not dimensioning arguments.  Especially make sure work areas
          are appropriately dimensioned.


     5.   Supplying incorrect 'row dimension' of matrices.   Many  NAG
          routines have a calling sequence of the form:

                        call sub( a, ia, n, ... )

          where 'a' is a matrix, 'ia' is it's first dimension  as  de-
          clared  in the calling program, and 'n' is it's order.  'ia'
          and 'n' are often different and must be specified correctly.