In the fall of 1972 President Nixon announced that the rate of increase of inflation was decreasing. This was the first time a sitting president used the third derivative to advance his case for reelection.

Hugo Rossi. Mathematics Is an Edifice, Not a Toolbox, Notices of the AMS, v. 43, no. 10, October 1996.

Welcome to the third part is the third part of the essential introduction to the FORTRAN programming series. In this part, we will introduce the use of functions and subroutines to structure the programs. Then we use them to make a program to calculate numerical derivatives of mathematical functions.