# Using excel to make plots

1. Oct 8, 2005

### Benny

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.

$$x_{n + 1} = \frac{{11.5x_n }}{{1 + x_n ^2 }} - \lambda ,x_0 > 0$$

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.

2. Oct 8, 2005

### hotvette

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 $x_{n+1}$. If you know lambda, all you need is a starting value for $x_n$.

Did I miss something?

3. Oct 8, 2005

### Benny

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. Oct 8, 2005

### faust9

Do you know how to use the quick fill corner?

5. Oct 8, 2005

### hotvette

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: Aug 20, 2007
6. Oct 8, 2005

### Benny

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. Thank you very much for your help.

7. Oct 8, 2005

### hotvette

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: Oct 8, 2005
8. Oct 9, 2005

### Dr Transport

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. Oct 9, 2005

### Andre

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. Oct 9, 2005

### Dr Transport

Cool.....Thanks