TI 89 Programming

I need to know if there is a way on the TI89 to input a fxn through a program and have that fxn go into the y editor.

ex: if i were to enter 1 + x; 1 + x would go into y1.

I know this can be done on the TI83Plus, and am trying to find a way to do this with the TI89.
on the TI83, I can do

Code:

Input "",Y1

but trying to do this on the TI89 gives me an error:

Code:

Input "", y1 or Input"", y2

I need to write this program for both calculators.

Unless, there is a way to do it on both calculators to enter a fxn such as:

dy
__ = x + y
dx

and be able to plug in x and y^2.

This is for Euler's method.

I don't want to program it as a flash app, as I would need a TI83 counterpart, and a similar program to both would be nice.

Thanks.

edit: All I really need to know is how to enter something and place it in y1

I used to program on a TI83Plus and inputting "32+a" as input
is completely legal. Not sure on a TI89, You could program it
in assembly.

That is where the problem lies. I don't really know assembly, and for some reason, I cannot get the SDK to run correctly on WinXP. Also, the Graph Link software is not compatible with the Graph Link USB.

It really is just the TI89 that I need to know how to do. I pretty much have the TI83 programmed, and it works. But the TI89 is giving me "variable name" errors.

You should have recieved a very VERY thick manual (i have one ), In wich all the programming keywords are listed, Theyre use and effects.

I did, it doesn't say anything about it in there.

I actually just ran into a problem with the TI83.

I'm trying to program Euler's Method.
The equation is

Code:

Yn = Yn-1 + f(Xn-1,Yn-1)Dx

where D stands for delta.

Now the problem resides in being able to do:

Code:

dy
___ = x + y
dx

How would I be able to enter this in, be able to solve an iteration such as (with X0 = 2, Y0 = 1); and x goes to 2.5 with 5 iterations:

Code:

Y1 = Y0 + (X0 + Y0)Dx
Y1 = 1 + (2 + 1).1

I don't know if this is possible.

Thanks.

not sure but I think you could do something along the lines of store the string. Then use Define Yn(x)=STRING
because when you type an equation into the y1= field the calculator just calls Define y1(x)=blah. Try typing an invalid equation into y1 and see the error you get.

Thanks for the help. I just changed my algorithm a bit. It works for both calculators.

For the TI89, I just made it to where the user must enter the equation first.

Thanks for the help Travis and Dalren.