Actually, HP 42s, Free42 and DM42 should have a standard interactive derivative function as the integral one, using custom menu:ferni123 wrote: ↑Sun Feb 07, 2021 5:09 pm

Then, how do you compute the 2nd derivative?

Step 0: Write the new function/program FF as explained above

Step 1: Type FF in Alpha register

Step 2: Type 2 in X-register

Step 3: Run DERIV function

Step 4: Set value of A in the menu with the number you like (type the value in the x-register and press the A option in the soft menu)

Step 5: Set the value of x where you would like to evaluate the 2nd derivative, for instance 1. (type 1 in the x-register and press the X option in the soft menu)

Step 6: Press again on the X option in the soft menu to indicate that you would like to derivative using the X variable

Step 7: You get in X-register the value of the 2nd derivative of FF evaluated in X=1

...

∂f(x)

menu -> choose function, choose order, choose point, choose accuracy -> result

Salvo