DER2.81 (Second Derivative) freeware
by Daniel Bishop (danb2k@hotmail.com)
2000-10-14
This program uses the centered difference formula to estimate the second derivative of a function (in this case, Y1), much like der2(y1,x,x) on the TI-86. To use this program, enter the function you wish to differentiate in Y1. Then, run the program and enter the value of X at which you want to evaluate the derivative.
Prgm_:DER2
:.001 -> E
:Disp "X="
:Input X
:X+2E -> A
:X-2E -> B
:-2Y1 -> D
:A -> X
:D+Y1 -> D
:B -> X
:(D+Y1)/4E² -> D
:Disp "DY1/DX="
:Disp D
Sample Run: find f"(3) if f(x)=x³
"X^3" -> Y1 // before running the program, store f(X) in Y1
Done
Prgm0 // substitute DER2's program number for the zero
X=
?3 // user input
DY1/DX=
18 // the derivative is 18, exactly the same as if done by hand