Dynamic Computation of Derivatives
It is shown how Wengert's procedure for computation
of derivatives can be implemented conveniently 
by use of compiler-generated complex addition, subtraction,
and linkage to complex arithmetic subroutines.
 Evaluation of a function and derivative proceed in
parallel, as in Wengert's procedure, but with the 
"imaginary" parts of variables declared complex bearing
the values of the derivatives of the real parts. 
 This technique provides a simple way to compute the
derivatives of a function, without the need for 
deriving and programming the evaluation of
explicit formulas for the derivatives.
CACM September, 1967
Lesk, A. M.
