Using excel to make plots

  • Thread starter Benny
  • Start date
  • #1
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Hi I'm currently working on an assignment and one of the questions requires me make a plot of the following. I am told that Excel can produce the plot but I don't know how to enter the equation.

[tex]
x_{n + 1} = \frac{{11.5x_n }}{{1 + x_n ^2 }} - \lambda ,x_0 > 0
[/tex]

A few values of lambda are specified. If there is a way to plot this on Excel? Any help would be great thanks.

Note: I hope this isn't the wrong forum for this question.
 

Answers and Replies

  • #2
hotvette
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I use Excel for plotting all the time, but there is no capability I know of to just give it an equation. What you have to do is calculate the x,y values, highlight them, and click the plot button.

Unless I don't understand correctly, this is just a set of parametric equations in lambda. What I'd do is have several columns, one corresponding to each value of lambda. Each row will be successive calculations of [itex]x_{n+1}[/itex]. If you know lambda, all you need is a starting value for [itex]x_n[/itex].

Did I miss something?
 
  • #3
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Yeah I've been given some specific values for lamda lie 0, 3, 6 etc. So if I wanted to plot this would need to calculate each value? As in for example I start with x_0 = 2. Then x_1 = some value. For the next point I would need to calculate x_2 = f(x_1) and so on? I just thought that there was some kind of shortcut to generating the values because I think that we're supposed to generate a whole bunch of values.
 
  • #4
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Do you know how to use the quick fill corner?
 
  • #5
hotvette
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Benny said:
Yeah I've been given some specific values for lamda lie 0, 3, 6 etc. So if I wanted to plot this would need to calculate each value? As in for example I start with x_0 = 2. Then x_1 = some value. For the next point I would need to calculate x_2 = f(x_1) and so on? I just thought that there was some kind of shortcut to generating the values because I think that we're supposed to generate a whole bunch of values.
Oh, but it is sooooo easy. Let me give you an example. Let's say x_0 is 2. Put that in cell A1. In cell A2, you want to calculate x_1, but I'll make up the formula just to make it simplier. Let's say x_n+1 = x_n^2 + 3*x^n + 5/3. In cell A2 you type (literally): =A1^2+3*A1 +5/3 and hit enter. Highlight cell A2, click copy, and highlight cells, A3 through A100 and click paste. That's all there is to it!
 
Last edited:
  • #6
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Oh ok, I didn't know that it could be done so easily. I'm pretty clueless when it comes to computers, apart from things related to fps.:biggrin: Thank you very much for your help.
 
  • #7
hotvette
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Check out the edit in my previous post. I gave an example of the very thing you are trying to do. Notice the formula has A$1. That means as you paste the formula down, the 1 remains fixed, meaning in this case, it is lambda.

Excel is one of the most amazing applications I have ever seen.

Check this out.

http://www.usd.edu/trio/tut/excel/
 
Last edited:
  • #8
Dr Transport
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hotvette,

how'd you get the formulas to show up in your attached picture?????

That is something I've been wanting to do at work to help check my analysis.....

dt
 
  • #9
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`Toggle formula's or values with <ctrl>+ ` that's the upper left key on my keybord, left of the "1", the graph accent underneath the ~.
 
  • #10
Dr Transport
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Cool.....Thanks
 

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