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#1 Ian

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Posted 22 March 2006 - 10:59 PM

Hi,

Does anyone know where i could get a freeware program that can draw graphs to an acceptable level for my investigiation? ie able to draw best fir lines and plot centroids etc.

Thanks

Ian

#2 Dave

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Posted 22 March 2006 - 11:36 PM

when i did i just used the graphs in excel. It can do best fits and error bars as required

If i am not here i am somewhere else



#3 broughy

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Posted 23 March 2006 - 12:01 AM

to be honest, excel is as much as you need. its what we use in uni for our lab work & lab reports, so you really don't need anything more technical than that. my one graph in my advanced higher investigation was drawn by hand, & yes, i passed it!
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cos you're the only one who can get me on my feet,
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#4 Vixus

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Posted 23 March 2006 - 10:13 AM

Yeah, I used excel for plotting a scatter diagram of results with error bars, then drew the line of best fit on myself. Remember to change the major and minor unit increments for the x and y axis though!

On the topic of graphs, how do I get uncertainty in a gradient if I've only got one line?

#5 Ian

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Posted 23 March 2006 - 04:50 PM

QUOTE(Vixus @ Mar 23 2006, 10:13 AM) View Post

Yeah, I used excel for plotting a scatter diagram of results with error bars, then drew the line of best fit on myself. Remember to change the major and minor unit increments for the x and y axis though!

On the topic of graphs, how do I get uncertainty in a gradient if I've only got one line?


you draw 2 lines parallel to the best fit line that pass through the most extreme points above an below. then you get a rectangle ABCD and work out the gradients AC and BD and slot them in some equaiton.

(Sorry it's hard to explain without a digram)

#6 skint_student

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Posted 24 March 2006 - 12:37 AM

Excel can automatically add a line of best fit, give you its equation and R^2 value.

The error in x is

= x SQUAREROOT[(1-R^2)/(n-2)]

where n is the number of plotted points

Dunno if thats cheating at advanced higher level but I'm a big fan of being lazy and getting excel to do everything.
Sorry if this doesn't make sense, I have no idea how to put equations on this thing.

#7 The Wedge Effect

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Posted 24 March 2006 - 01:22 PM



\begin{align*}error\,in\,x=x \sqrt \left({\frac {1-R^2}{n-2}\right)}\end{align*}

Yeah, decided to clarify because I was bored. tongue.gif

#8 AppleCore

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Posted 24 March 2006 - 01:27 PM

I posted this up

Edit: I thought i sent u a copy of this???

#9 broughy

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Posted 24 March 2006 - 11:58 PM

QUOTE(skint_student @ Mar 24 2006, 12:37 AM) View Post

Excel can automatically add a line of best fit, give you its equation and R^2 value.

The error in x is

= x SQUAREROOT[(1-R^2)/(n-2)]

where n is the number of plotted points

Dunno if thats cheating at advanced higher level but I'm a big fan of being lazy and getting excel to do everything.
Sorry if this doesn't make sense, I have no idea how to put equations on this thing.



QUOTE(The Wedge Effect @ Mar 24 2006, 01:22 PM) View Post



\begin{align*}error\,in\,x=x \sqrt \left({\frac {1-R^2}{n-2}\right)}\end{align*}

Yeah, decided to clarify because I was bored. tongue.gif




yeah - what they said! lol. i seem to remember having to do it a complicated way with boxes & stuff at advanced higher. however, the excel way is far easier & its what i'd use now.....but that is possibly only cos we did actually get about 5 dedicated "errors lectures" in uni this year huh.gif
when i'm dancin' with you,
tomorrow doesn't matter,
turn that music up,
till the windows start to shatter,
cos you're the only one who can get me on my feet,
& i can't even dance

No Tomorrow - Orson

#10 Vixus

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Posted 25 March 2006 - 01:50 PM

QUOTE(skint_student @ Mar 24 2006, 12:37 AM) View Post

Excel can automatically add a line of best fit, give you its equation and R^2 value.


How?! How?! biggrin.gif

#11 skint_student

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Posted 25 March 2006 - 02:58 PM

QUOTE(Vixus @ Mar 25 2006, 01:50 PM) View Post

QUOTE(skint_student @ Mar 24 2006, 12:37 AM) View Post

Excel can automatically add a line of best fit, give you its equation and R^2 value.


How?! How?! biggrin.gif



When you have plotted your graph right-click on your data points, then select "Add Trendline". Select whether it is a linear or exponential graph or whatever, then go to "Options" and tick the boxes to display equation on chart and R squared value. Then click "Ok" and you magically have your line of best fit all done for you biggrin.gif

#12 Vixus

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Posted 27 March 2006 - 10:41 PM

Amazing!

#13 smit

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Posted 28 March 2006 - 03:24 PM

I dont understand, I have always been made to use random error,

range/number of measurements

As my error bars, what does the error in x equation do?

And what is R?

#14 Vixus

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Posted 28 March 2006 - 03:44 PM

smit, that's used to find error in the gradient.

#15 broughy

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Posted 28 March 2006 - 09:20 PM

QUOTE(smit @ Mar 28 2006, 04:24 PM) View Post

I dont understand, I have always been made to use random error,

range/number of measurements

As my error bars, what does the error in x equation do?

And what is R?


R^2 is a value that you can get excel to give you on best fit straight lines. you use it in the equation quoted above to work out the error (i believe its the random error? hopefully someone can correct me if i'm wrong). in the gradient of the graph. for example, in some experiments the value for the gradient corresponds to the property that you're trying to obtain a value for, & in this case, the error in the gradient would be the error in this value.
when i'm dancin' with you,
tomorrow doesn't matter,
turn that music up,
till the windows start to shatter,
cos you're the only one who can get me on my feet,
& i can't even dance

No Tomorrow - Orson





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