Help Needed by Maths literate person

[Brian d marge]

Hi folk
I posted this under tuning as eventually thats what the above will be used for ......
What I need help with is help with intergration ....I was to busy looking up the skirt of the maths teacher ,,,,and that was a few years ago now .....

Anyway ... I need to find the area under the/ Binomial ( an upside down U just incase I got the name wrong ....
What I would like to do Is use intergration to arrive back at the equation of the graph ,,,,

Whats happening is I am getting the data ,,,constucting /plotting the graph ..then I can find the area ( Use acad and ask for the area ....!!!!) ,,,but it doesnt give me the equation ,,,which in some circumstances could be of use .....
Anyone Know of a method of working back to find the equation and hence the area ?????
Its worth a punt ,,,,,,( and before anyone asks I did a google search ,,,but me x s and Y s ,,,fell apart ,,,as it wasnt easy to understand ,,,,)

thanks in advance I hope some one can point me in the right direction ,,,,,

Stephen

who also hasnt access to any text books ,,,,,,

[erik]

you want the equation for the curve that fits the data?

Or you want teh equation for the area under the curve?

If you have excel, to get the equation for the line that fits the data, make an XY (scatter) plot graph, then go to the chart menu and "add trendline" and you can choose what type you want (polynomial, I guess.) and make sure you click the next tab on the window and select "show equation on graph"

If you haven't got excel, I dunno how you'd do it

[ZorsT]

the curve you speak of sounds like a parabola. (a -ve one at that)

If I had my books here I might be able to tell you.

I'm not sure if 6th form is enough though

[sAsLEX]

what eric said is the goer for the equation of the line, then its integration of that to find the area, also a pic always helps! post it up here there are enough of us engine-neers here to try sort it out

[marty]

it's 42. everyone knows that.

[marty]

oops sorry gareth - i've gone off track. my apologies.

[Drum]

Sounds like a polynomial equation (-ax^2-bx-c) picture needed.
Area doesnt matter as that area could be bounded by any number of equations.More helpful to provide a few sets of co-ordinates. Then it can be solved.

Or as previously mentioned. Plot it in excel. Add a polynomial 'trend line', then right click the trendline, go to options, and click display equation on graph.

[R6_kid:Me]

oops sorry gareth - i've gone off track. my apologies.

how did you know i was watching!!! i was thinking the exact some thing, 42 is the answer to the universe, life, and everything...

its not off track, tis good humour

now what im doing is....

stephen - put a pic up and i'll see if my D- in Maths 108 (calculus) can help you at all

[Brian d marge]

you want the equation for the curve that fits the data?

If you haven't got excel, I dunno how you'd do it

dunno about having Excel....I havent a clue ....that doesnt help matters !! but yes I will post a pict when I get home

Stephen

[T.W.R]

have worked with excel quite a bit and don't really think you'll be able to calculate a specific arethmetic progression or volume through excel unless you have the complete data range of the parabolic curve( i presume thats what your working with) and know the set points/area of the curve you want unless you use a isological or isref calculation in excel.
you may have to use a CAD program to identify the points for calculation
ie. excel can't equate volumetric sequences or measurements into a true figure

[FzerozeroT]

Hmm, could help if you were a bit more specific about the data gathered, i.e. if it is the resonant value of an exhaust etc, because you need to make sure that the equation has a distingushable variable for each physical thing. Sampling errors could give you a polynomial that is missing a factor such as airbox resonance/volume, and you'll end up using a bollox equation. Or ignition mapping??

[Brian d marge]

Ok..hope this works ..BTW thanks for the response terriffic ...Mongo ere aint to good wiv da numbers ,,,I just hit em wiv big ammer till they look good ...Eric can vouch for that !!!

hope the attached file helps

I use acad at the moment ,,,but one day Im not going to have access to acad ,,so really must learn the method ..( again ..was to busy looking up teachers skirt ,,,,can remember her clearly ...black stockings ,,little black dress,,,must of dropped me pencil a thousand time a class.....)

So yeah both the area under the graph ..( ralf half pissed as a newton method ..adding squares ...
and the equation of the line would be great .....

Thanks Stephen

Stephen

[Drum]

Brian, do you have the raw data in some sort of file? If so, post that instead.

[avgas]

How far apart are the data points brian? cos if they are close enought to be accurate then you can use the simple summation rule.
ie add all the totals together to give you the total area. There looks to be sufficent resolution of data points to do that and will get you to within .01mm of the actuall integration.
If you give me the raw data i can probably punch it through MATLAB if i still remember how to use damn program....cursed black magic.

[Jeremy]

As nice as the data plot is the raw data would be far more useful.

Your best bet is probably to use Simpson's rule even though chances are your function isn't a polynomial with a degree of cubic or less. [Looks like a sine function with a simple transform to me]