The physical problem is that of case (100), effected by:
L(100)
    but the Gauss-Seidel solver is activated, in place of the
    Stone-type default, by the following commands:
TEXT(3D Heat Cond. Gauss-Seidel Solver 
TITLE
libref=103
USOLVE=T;CSG3=GAUS;LITER(TEMP)=-125