Programming functions

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Programming functions

zEcho1 19 Feb 2021 16:48

Hello

So I am working on a school project and I was wondering if there was a way to make a program that asks you to insert a function equation, together with an x variable. I want to have the calculator use that x variable to fill the equation in and return you the y value.
I need this to program something else which I have in mind.

I am a novice when it comes to programming but I catch on things quickly, if you can give me an idea or example of how to do it I will be sure to pick it up!

I am using a Ti-84 and the "Ti Connect CE" app to program my calculator.

Any help is very appreciated!

Thanks.

Last edited on 19 Feb 2021 16:49 by zEcho1 Show more

Re: Programming functions

Mr Bob Jr IV 19 Feb 2021 22:35

Hopefully this answers your question!

If you have a function stored to one of the Y= variables such as Y₁, you can use the notation Y₁(X) to return the y-value for a corresponding x-value. So simply ask the user to input a value for X, then display Y₁(X).

If you want the user to input a function during the program, instead of using one that was previously typed into the Y= page, you can use the Input command! Doing this

Input "Y₁:",Y₁

will take what is entered and store it to Y₁. However, using the Input command to store to Y₁ requires the user to put quotes around the function when they type it in, which I find annoying and unintuitive. Instead, you can do

Input "Y₁:",Str1
StringEqu(Str1,Y₁

This stores to a string variable, which doesn't need to be entered with quotes around it, and then stores that string to Y₁. The code is longer but provides a nicer experience, so take your pick!

Re: Programming functions

zEcho1 20 Feb 2021 09:18

Thank you for the answer!

I've played around with it and the 2nd one seems to be working perfectly, which I am thankful for.

To clarify what I am trying to do, I am trying to program the calculator into finding the tangent line of an equation I have given one point.
I know the formula y = Df(a)(x-a) + f(a) and I am trying to make usage of that.

Input "Function:",Str1
StringEqu(Str1,Y₁
Input "Derivative:",Str2
StringEqu(Str2,Y₂
Input "X=",Z
Y₂(Z)(X-A)+Y₁(Z)→Y
Disp "Y=",Y

This is what I currently have, this seems to be working well excluding the fact that it is giving a certain value to "X" and not leaving it just as "X"

For example it returns me "Y= 5" (Because it assumes that x = 0?

Is there a way to go around it or is it impossible?

Thanks

Edit: if not, is there a way to use matrices and display the coefficients or something similar, perhaps?

Last edited on 20 Feb 2021 09:58 by zEcho1 Show more

Re: Programming functions

Mr Bob Jr IV 20 Feb 2021 21:20

You are correct, the calculator thinks you want to use the value of X instead of leaving it as the letter "X". To fix this, you have to split it into number parts and letter parts. The Disp command would put each part on a separate line, so instead you can use the Output command to display each part on a specific point of the screen (such as all on one line!)

Output(1,1,"Y=     (X-     )+")
Output(1,3,Y₂(Z))
Output(1,11,A)
Output(1,18,Y₁(Z))

In this example I put 5 spaces between each part so that it will show up to five decimal places of the values, but you can adjust the number of spaces and the starting column (the second argument of the Output command) to make the numbers show up exactly how you want!

Two quick notes: For clarity I included the closing quotes/parenthesis on the end of each line, but to save space you can remove them, since the Output command works without them! Also, there may be a more complicated but more efficient way to achieve this same result by using the toString command. If you're interested I can explain it, or feel free to check out the toString command page for more info!

Re: Programming functions

J_Walker87 21 Feb 2021 01:47

You can use the nDeriv( function to find the derivative at a point. This function is very helpful in my AP calculus class, and by using it in your program you could make it so that the user doesn't have to enter the derivative of the function. You can find documentation for the nDeriv( function by looking it up in this wiki's command index. I was able to make a tangent line finder that only required the user to enter the function and the x value by using the nDeriv( function, so I highly recommend using it in your program. Let me know if this works for you!

Re: Programming functions

zEcho1 05 Mar 2021 14:32

Hello

First of all, thank you for your replies. I've been moving out recently and I had no access to the cable that connected my calculator to my pc which made me unable to test out any program I made.

Either way, I've changed my code to the following:

Input "Functie:",Str1
StringEqu(Str1,Y₁
Input "X=",Z
nDeriv(Y₁,X)→D
Output(1,1,Y=     (X-     )+)
Output(1,3,D)
Output(1,11,A)
Output(1,18,Y₁(Z))

but this gives me an "argument" / "syntax" error.
I've also tried playing around with the "Output(" command but whenever I run such program as:

Output(1,1,"test

it only returns "Done" and does nothing.

Thanks.

Last edited on 05 Mar 2021 14:34 by zEcho1 Show more

Re: Programming functions

Mr Bob Jr IV 05 Mar 2021 20:13

The argument error is caused by the nDeriv() command, because the command can only find the derivative at a specific point along a curve, so you need to say the x-value where you want to take the derivative. In this case your x-value is stored to Z, so include that in the command:

nDeriv(Y₁,X,Z→D

The syntax error is being caused by a missing quotation mark in line five, right before the Y=.

I am sorry to hear the Output command wasn't working for you, I am not sure why. My only idea is that it showed up on screen but overlapped some other text so you didn't see it. If you use the command ClrHome at the beginning of the program it will clear the home screen so you can easily see everything that you output.

Re: Programming functions

zEcho1 06 Mar 2021 12:12

After playing around with it, I came up with the following program:

Input "Functie:",Str1
StringEqu(Str1,Y₁
Input "X=",Z
ClrHome
nDeriv(Y₁,X,Z→D
Output(3,1,"Y=  (X- )+")
Output(3,3,D
Output(3,8,Z
Output(3,11,Y₁(Z)
Output(3,13,"

The only issue is that whenever I am using functions that return me large values, those values end up taking most space on the screen and nothing gets projected the way it should.
Do you have any idea of how to fix it? Perhaps we should round our numbers, or maybe out put each value on a separate line?

I was also thinking of giving the equation in standard form and then project below it the values that should be inserted where they should, that seems like a good fix as well? I definitely prefer the prior solution but if there is no other way then I don't really mind doing that.

Thanks

Re: Programming functions

CalcNerd 06 Mar 2021 12:49

Not sure if this will completely solve your problem, but you can use Disp instead of all the Output commands. It will make it cleaner and put everything on different lines.

Disp "Y=  (X- )+"
Disp "D=",D,"Z=",Z,"Y₁(Z)=",Y₁(Z)

Re: Programming functions

J_Walker87 08 Mar 2021 23:57

I agree with CalcNerd on that. Also, Ti-Basic will display the value produced by the last line of code instead of the "Done" message if it can, which means you'll be able to just put Y₁(Z) at the end of your program instead of "Disp Y₁(Z)" if you choose to use the Disp command. This could potentially solve the problem with the "Done" message.