WP 34S problem in solving f'(x)=0

[Dieter]

(02-18-2015 02:11 AM)Paul Dale Wrote:  It is case insensitive in both the delta and the x. I don't recommend having several differently named versions around.

Then the manual should also reflect this. My 3.2 version says:

Quote:f’(x) will look for a user routine labeled 'δx', returning a fixed step size dx in X.

If both delta and X are case insensitive I think this is an important detail that has to be mentioned. Otherwise the user may code a program starting with label ΔX, being confident that it does not interfere with the derivative functions as they require "...a user routine labeled 'δx'". Typing an uppercase "ΔX" also is easier and faster. Walter: please update the manual in this regard.

I would also suggest a different ΔX default value. The current 0.1 can be too large for many applications as the function is evaluated at x±5Δx. Something like the way I suggested should work better, i.e. x/1000 resp. 0,001, maybe rounded to one or two significant digits.

BTW what is the sequence the derivatives search for the delta-x label? δx → δX → Δx → ΔX? I also think it would make sense to demand a fixed uppercase label ΔX. This is the easiest version for the user and it frees three other labels to be used for other purposes. And it saves some memory and time since the derivatives do not have to search for four different labels.

Dieter