If using this code for research or industrial purposes, please cite:
Emilio Martinez-Paneda, On the finite element implementation of 
functionally graded materials, Materials 12(2): 287 (2019)

Temperature.inp showcases the graded element implementation using the
temperature as an auxiliary field. The temperature variation is defined
through a predefined field and an analytical field: dexp(2.07944154168*x)

USDFLD.inp showcases the graded element implementation by means of a
user element subroutine (USDFLD.for) to the material gradient at the
Gauss integration points.
