V4ITD - A PORTABLE AND EFFICIENT FORTRAN IMPLEMENTATION OF THE 4IT ALGORITHM USING VIRTUAL MEMORY AND AN EXTERNAL STORAGE DEVICE

V4ITD is a FORTRAN subroutine which does the four-index transformation of atomic and molecular physics by means of the 4IT algorithm described in the previous paper, and which requires enough virtual memory to store all intermediate quantities. Depending on the size of a given block of integrals and on the amount of central memory, an internal sort or a portable FORTRAN external sort library is used to carry out a localization of pertinent data sets. V4ITD is also more general than C4ITD: any number of blocks of integrals may optionally be read as incomplete dual lists of orbital indices and numerical values residing in an external file, in which case the final blocks of integrals are delivered also as dual lists into an external file.