It is possible to add a set a new built-in functions to Scilab by a permanent link the interface program. For that, it is necessary to update the files default/fundef and routines/callinter.h.
When intersci is invoked as follows:
intersci <interface name><interface number>
intersci then builds a .fundef file which is used to update the default/fundef file.
To add a new interface the user needs also to update the routines/callinter.h file with a particular value of fun Fortran variable corresponding to the new interface number.
Two unused empty interface routines called by default (matusr.f and matus2.f) are predefined and may be replaced by the interface program. Their interface numbers 14 and 24 respectively. They can be used as default interface programs. The executable code of Scilab is then made by typing ``make all'' or ``make bin/scilex'' in Scilab directory.