Midmotorsteve

Help, i have 5 points along a scale of 0 to 25 (x axis)that are not whole numbers i.e 1.5625, 3.125, 6.25, 12.5 & 25 attached to each value is another value (Y axis) i want the x axis to show increments of 1,2,3,4,5,etc up to 25 but i can't seem to make it happen any one help me, i need it sorted but the morning, pleeeasee

Also anyone know how to make excel calculate the area beneath a curve of a graph???

i have my faith the technical guys here!! give answers

thanks

Steve

Midmotorsteve

ok just need to know how to calculate area beneath a curve on a chart now....some one...please

Country Boy

Steve,

As far as I know, there is no function in Excel to calculate the area under a graph. Assume you found the XY plot option for your first question, are you trying to calculate the area under that graph, or something more complex?

Jimbo

-=Buzz=-

thats blummin advanced maths that is, not a spreadsheet function.

I used to have a calculator that would calculate the area under a curve from the equation used to produce it.. Cant remember the damn word for that type of thing... grrrrr.... its on the tip of my tongue..

There IS a long winded way of doing it to get an approximate answer. Draw the graph to scale on some graph paper, and actually COUNT the squares under the curve, including estimating the sixe of the incomplete ones! This WORKS, trust me, but isnt exact to lots of decimalsas you can guess.

-=Buzz=-

here you go - its Integration that you want to do, look at the sub heading " Areas " about a third of the way down.

You want the area under the arc of a parabola Im guessing.

See, Im brill me

http://archives.math.utk.edu/visual....s/4/index.html

[Edited by -=Buzz=- - 3/24/2003 10:30:02 PM]

Country Boy

Buzz,

Dead right, it's integral calculus you need to find the area under a curve. We have to use it all the time at work, and have some very clever software (expensive!) to do it for us, but if steve just needs to find the area under a 5 point graph, it is just a question of rectangles and triangles.

Jimbo

Dan B

Do you have the equation for the relation? e.g. y=ax+b

If so I'll do the maths for you basic A-level stuff really. I assume you want the area from 0-25?

TopBanana

Yeah, equation would be useful! Or the datapoints you have if you want an approximate figure

ajm

If you have the formula for the graph then you can integrate as someone said above, or use iterative methods on a pc that will divide the area up into small strips then add them together.

Alternatively you can use the points you know to get an approximate area using trapeziums.

If you don't have a formula for the graph then Excel has some curve fitting algorithms that should get you a fairly decent formula that you can then use the above on.

I am not aware of a function in excel that does integration, but its possible to write an iterative solution using VB in Excel.

Midmotorsteve

cheers guys,

in the end i cheated, as i had three curves, one a standard and 2 i needed to compair to it, so i printed them, cut them out and weighed the paper. That way i could compair them %age wise, i thought about counting squares but then realized i didn't have any graph paper.

Excel should have a function for this, it was to calculate Glycaemic Index values for bananas and chick peas, with reference to glucose syrup. Post grad Applied Biomedical Science.

it was a 5dp digi scales so shouldn't be to way off

thanks...never actually got the area tho