How to plot an integral on Prime?
02-28-2017, 11:53 PM (This post was last modified: 02-28-2017 11:55 PM by TheKaneB.)
Post: #1
 TheKaneB Member Posts: 175 Joined: Jul 2014
How to plot an integral on Prime?
Hi,

I'm trying to plot the integral of a function, just like this: http://www.wolframalpha.com/input/?i=plo...x+of+x%5E2

I can do it very easily with Wolfram / Mathematica, and the TI calcs also work but they are slow.

I tried this on my Prime:
CAS.int(x*x, x, 0, x)
but all I get is a Syntax Error.

If I try to enter the function using the Integral graphical template, it will enter, but the plot is empty and the Numerical Table is full of NaN.

PS: It would be nice to plot this also in my 50g. I'm struggling with it, which is a shame since it's my favourite calc!

Software Failure: Guru Meditation

--
Antonio
IU2KIY
03-01-2017, 01:10 AM
Post: #2
 TheKaneB Member Posts: 175 Joined: Jul 2014
RE: How to plot an integral on Prime?
Update:

on the 50g I've found a way to plot the function I want:
y(x) = INTVX(f(x)) - INT(f(x), x, 0)

Example: on the TI-89 I plot: ( I will use $for the integral symbol) y(x) =$(ln(x), x, 0, x)

and on the 50g:
y(x) = INTVX(LN(x)) - INT(LN(x), x, 0)

On the 50g the function entry is quite tedious, BUT it's many times faster than the TI. While the TI has drawn the first 2 pixels, the 50g has already finished the whole graph 3 times in a row But still no luck on the Prime Honestly, I'm getting tired of this calculator... If I can't solve this issue I'll stick to my 50g for everything

Software Failure: Guru Meditation

--
Antonio
IU2KIY
03-01-2017, 01:56 AM
Post: #3 Han Senior Member Posts: 1,883 Joined: Dec 2013
RE: How to plot an integral on Prime?
1. Press the [Apps] key. Select the Function app.
2. Press [Symb] and enter in: $$\int$$(T^2, T, 0, X) (in algebraic entry mode) or $$\displaystyle \int_0^X T^2\ dT$$ (in textbook entry mode)
3. Press [Plot]

You cannot use the X for your variable of integration because the system uses X as the input variable of the function being plotted. It evaluates the formula at various values of X, but it cannot do so if your formula is $$\int$$(X^2,X,0,X).

Think of it this way:

If $$\displaystyle f(x) = \int_0^x x^2\ dx$$ then would
$f(2) = \int_0^2 2^2\ d2$
make much sense? (Pay attention to the differential "$$d2$$")

Graph 3D | QPI | SolveSys
03-01-2017, 02:20 AM (This post was last modified: 03-01-2017 02:31 AM by TheKaneB.)
Post: #4
 TheKaneB Member Posts: 175 Joined: Jul 2014
RE: How to plot an integral on Prime?
It works, thank you!
Now I have another problem.

I tried to plot the integral from 0 to x of tan(t^2) and it's stuck forever. Keyboard and screen are unresponsive, [Esc] and [On] keys don't seem to stop the computation.

After 2 minutes I decided to reset, then I tried again in Table view ( [Num] key ) and at least it's calculating correctly. Maybe it's just too heavy of an integral for the plot view.

Anyway, this is another issue. Thanks again!

EDIT: Your explanation is spot on, I tought that the HP would substitute the 'x' only inside the expression, but that would require a special case to handle the integral correctly. I wonder if TI and Wolfram did a special code path just for the integral, it would make sense for an educational market.

Software Failure: Guru Meditation

--
Antonio
IU2KIY
03-01-2017, 03:13 AM (This post was last modified: 03-01-2017 03:14 AM by Han.)
Post: #5 Han Senior Member Posts: 1,883 Joined: Dec 2013
RE: How to plot an integral on Prime?
Try this alternate method:

In the CAS, create a function like so:

f(x):=int(tan(t^2),t,0,x);

Then in the [Symb] view, use f(X) as your formula. (Note upper vs lower case) I generally prefer this method since it means I can use the function f for other calculations as well as graphing.

Graph 3D | QPI | SolveSys
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