Equilibrium Spline Interface ( ESI) for magnetic confinement codes

Additional comments: The main file esiXZ.c with ESI routines is described in the main text. Two (C and FORTRAN) programs C2esi.c, F2esi.f demonstrate the generation of ESI data files. Four other demo programs, linked with esiXZ.c demonstrate the use of the interface in magnetic flux coordinates ( demoC.c, demoF.f) and in laboratory cylindrical coordinates r,z ( RZdemoC.c, RZdemoF.f).