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Graph problem
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timijan


Newbie


Joined: 26 Jun 2011
Posts: 21
Posted: 28 Jan 2012 02:01:41 pm    Post subject: Graph problem
Hey,

I got a problem with plotting a function stored in a variable.

For example:

x+2 -> w
Graph w

but this doesn't work. What am i doing wrong or is this even possible?
(TI 89T)
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KermMartian


Site Admin


Joined: 14 Mar 2005
Posts: 55879
Location: Earth, Sol, Milky Way
Posted: 28 Jan 2012 02:03:03 pm    Post subject:
Can I safely assume that you're using a TI-89 here, Timijan? W is a number, not an equation, so you'll be literally storing the value of x plus 2 into w; this means you'll get a horizontal line when you graph it. You instead want to store the equation "x+2" into one of the graph functions and graph that.
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Ashbad


I am governor Jerry Brown


Joined: 01 Dec 2010
Posts: 2423
Location: There lived a certain man in Russia long ago
Posted: 28 Jan 2012 02:03:22 pm    Post subject:
You actually aren't storing an equation into that variable, you're actually storing the value of X + 2 into W. Is this in a program, or just in general with the equation inputter/graph button?
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-Ashbad
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timijan


Newbie


Joined: 26 Jun 2011
Posts: 21
Posted: 28 Jan 2012 03:32:56 pm    Post subject:
@KermMartian indeed i am using TI-89. You managed to replay before i could edit my post Smile

@Ashbad i try to use this in a program.

Based on input data and some derivation function is formed and than i try to graph that function.

Now if i try to put this function in "x+2"-> w and graph w, nothing happens. Graph screen is shown but nothing is drawn. If i try to store it in y1 instead of w it says name is reserved.

So even though i thing what i was doing wrong, i still don't know how to make this work.
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timijan


Newbie


Joined: 26 Jun 2011
Posts: 21
Posted: 29 Jan 2012 05:45:59 am    Post subject:
Ok, I managed to sole it like this:


Code:
x+2->w
string(w)->w
"Define y1(x)="&w->q
expr(q)
DispG
Pause


Last edited by timijan on 29 Jan 2012 02:11:47 pm; edited 1 time in total
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KermMartian


Site Admin


Joined: 14 Mar 2005
Posts: 55879
Location: Earth, Sol, Milky Way
Posted: 29 Jan 2012 11:09:18 am    Post subject:
I wrapped your code in [code] tags, good sir. Yup, that's a good way to do things, although why can't you just directly run the Define command?
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CharlieMAC


Advanced Newbie


Joined: 02 Jan 2012
Posts: 58
Posted: 01 Feb 2012 08:52:09 am    Post subject:
I have a similar problem. I want to plot a function (particularly, a polinomial) which depends on the variable t. the polinomial is stored in the variable p, so according to the user's guide I should proceed like this:


Code:
graph p, t


But when I do this it gives me an error that says "Undefined Variable". I also tried the solution timijan found but it didn't work.

Any idea?

Thanks in advance
Charlie
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KermMartian


Site Admin


Joined: 14 Mar 2005
Posts: 55879
Location: Earth, Sol, Milky Way
Posted: 02 Feb 2012 01:31:18 pm    Post subject:
Have you tried the obvious solution of checking that p is defined? Are you sure you don't have to put the t in quotes?
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Travis


Advanced Member


Joined: 03 Feb 2011
Posts: 218
Location: Kansas, USA
Posted: 02 Feb 2012 02:49:41 pm    Post subject:
The Graph command wants an equation entered exactly the same way it would be entered on the Y= screen. You can either do something like:

Graph x+2,x

to graph x+2. Or, you can define the function in a separate variable:

Define w(x)=x+2

and then:

Graph w(x),x

This syntax should work. Make sure the graphing mode in the Mode screen is set to Function first.
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CharlieMAC


Advanced Newbie


Joined: 02 Jan 2012
Posts: 58
Posted: 02 Feb 2012 08:12:45 pm    Post subject:
It's weird. If I execute for example:


Code:
graph 2*t + 1, t


From the home screen, the calculator plots the function 2*t+1, but if I put it in a program it gives an error saying "Undefined variable".

I solved the problem I had, but I had to do this:


Code:
"define pos(t)="&p
graph pos(t),t



Where p is an expression that depends on t and it was previously defined.
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Travis


Advanced Member


Joined: 03 Feb 2011
Posts: 218
Location: Kansas, USA
Posted: 03 Feb 2012 05:56:39 am    Post subject:
CharlieMAC wrote:
It's weird. If I execute for example:


Code:
graph 2*t + 1, t


From the home screen, the calculator plots the function 2*t+1, but if I put it in a program it gives an error saying "Undefined variable".


Do you happen to have ‘t’ defined as local with the Local command? It seems that this will cause the error. If so, removing it from Local may help.
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CharlieMAC


Advanced Newbie


Joined: 02 Jan 2012
Posts: 58
Posted: 03 Feb 2012 08:38:01 am    Post subject:
Travis wrote:
CharlieMAC wrote:
It's weird. If I execute for example:


Code:
graph 2*t + 1, t


From the home screen, the calculator plots the function 2*t+1, but if I put it in a program it gives an error saying "Undefined variable".


Do you happen to have ‘t’ defined as local with the Local command? It seems that this will cause the error. If so, removing it from Local may help.


I tried both things (t as local and not local), but none of them worked.
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