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How do I enter a d/dX function such as d(sin X)/dX into the graphing app to plot? I keep getting a plot where f(X)=0 for all X.
(01-14-2017 07:33 PM)lrdheat Wrote: [ -> ]How do I enter a d/dX function such as d(sin X)/dX into the graphing app to plot? I keep getting a plot where f(X)=0 for all X.

This is not a dumb plotting question at all. I thought using the Function app command SLOPE would work:

SLOPE( f(X), X ) but all zeroes are plotted. That shouldn't be happening.

A way to plot the derivative, but two function slots will be needed:

F1(X) = f(x), unchecked (or checked if you want)
F2(X) = ((F1(X) + dx) - (F(X) - dx))/dx (checked)

dx is small, like dx = 0.01 or 0.001. You can make dx smaller but I find using the definition of the derivative for simple problems, 0.01 and 0.001 work well.

Example:
F1(X) = 2*X^2
F2(X) = ((F1(X) + 0.01) - (F1(X) - 0.01))/0.01

There are other derivative numerical formulas if needed.

I hope this gets addressed for the next Prime update.

Eddie
(01-14-2017 07:33 PM)lrdheat Wrote: [ -> ]How do I enter a d/dX function such as d(sin X)/dX into the graphing app to plot? I keep getting a plot where f(X)=0 for all X.

Type: F1:=diff(SIN(X),X); [ENTER] at the command line, then press the Plot button. I am not sure you can simply enter in diff(SIN(X),X) in the Symb view because it does not evaluate the definition, unlike the command line. In other words, typing F1:=diff(SIN(X),X) at the command line evaluates the right hand side and thus defines F1(X) as COS(X). Typing it in the Symb view creates F1(X) as diff(SIN(X),X) (since there is no evaluation) so that F1(1) is diff(SIN(1),1) and is therefore non-sensical.
Hello,

The best way is to use the CAS as described above. you can even simplify by doing F2:=F1'

This is best because it is the least amount of work and because the calculation of the function for drawing will be very fast...

Else, you can enter F2 as
d(F1(X))/d(X=X)
where d is the derivative symbol (use the template in the template key)....

I know that it might look strange at first, but you need to realize that the evaluation of d(F1(X))/d(X) is a FUNCTION, not a number! hence, if you were using this as a definition of F2, in every point, F2 would evaluate to a function and not to a number.
in fact, the X in the F1(X) and the first X are NOT the same as the X on the right side of the = sign... that X is the X that the function is evaluated for, the other is the derivative variable.

Best would be to enter d(F1(A))/d(A=X) or something like that, but this is more keys :-)

note, that this solution is slower as the derivation has to be performed for every point!

Cyrille
Thanks!

Great explanation!
Now that I know how to plot d/dx of a function in the graphing app, how do I accomplish this in the advanced graphing app? I keep getting an invalid object message. Physical Device.
I like dumb piloting questions, but this wasn't one :-)
(01-20-2017 05:56 AM)Geoff Quickfall Wrote: [ -> ]I like dumb piloting questions, but this wasn't one :-)

Dammed auto-correct.
It's good to know that "piloting" questions are given priority in answering though.
Geoff autocorrects to Goof. :-)
(01-20-2017 07:30 AM)Den Belillo (Martinez Ca.) Wrote: [ -> ]
(01-20-2017 05:56 AM)Geoff Quickfall Wrote: [ -> ]I like dumb piloting questions, but this wasn't one :-)

Dammed auto-correct.
It's good to know that "piloting" questions are given priority in answering though.

Thank you for explaining that...
I was beginning to think I wasnt going to pass my PPL (Private Pilots Licence) .
Wow! Did not see that auto correct had changed my topic to piloting! ?

Does anyone know how to plot a d/dx plot in the advanced graphing app?