cfu (Climate Fortran Utilities) package need to be compiled for the subchain scripts.
Change into the CFU source code directory:
cd /$SPDIR/src/cfu

Open the Fopts script with any text editor and change the fortran options according to your computer platform. Compile CFU:

If compilation is successful an executable $SPDIR/src/cfu/bin/cfu is created.

Usage:cfu <function> <function argument 1> <function argument 2> … <function argument n>