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Numerical integration in Excel

Posted on 1998-02-18
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Last Modified: 2008-03-03
Is it possible to integrated a column of values in Excel?  If so, how?
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Question by:BoB
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Expert Comment

by:frazer
ID: 1610100
Hi bob

assuming you want the numbers to increment in column 'A' do
1)  In cell A1 type     1
2)  In cell A2 put the formula =A1+1
3)  Copy the formula down as far as you need to
4)  If you need the cells to contain text values not formulas copy the entire column and then paste special values over the top.

Hope this helps

Frazer
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Author Comment

by:BoB
ID: 1610101
This only works for special cases and is not valid for most functions.  Try putting 1-10 in column A, then 2*A1 in column B and then your integration strategy (B1 in C1, then B2+B1 in C2) and you will notice that C10 has the value 38 however the integral of 2*x from 1 to 10 in 99.
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Expert Comment

by:frazer
ID: 1610102
Hi, Bob

I do not understand what you are trying to do

can you give me more detail of exactly what you want in each of the cells in the spreadsheet.

Thanks

Frazer
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Author Comment

by:BoB
ID: 1610103
Column A [1,2,3,4,5,6,7,8,9,10]  
Column B [1,4,9,16,25,36,49,64,81,100] {B=A^2}
Column C integral of B=A^2 which is (1/3)A^3 so in each row
         [1/3,8/3,27/3,64/3,125/3,...]

Now, that is easy to do if you have functions like I have in this example, but if the data in column B is not a mathematical function, how can I integrate it?
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Expert Comment

by:frazer
ID: 1610104
Hi,

I more understand what you are trying to do now but it is a few years since i have done any intergration.

what other than a numerical function are you trying to intergrate?

the formulae you have provided above work without any problems.

i used....

1 in cell A1
=1+A1 in cell A2
copied the formula down so cell A10 is =1+A9
then in column B
=A1^2 in cell B1, although i thought it should read =(1/2)A1^2
copied the formula down so cell B10 is =A10^2
then in column C
=(1/3)A1^3 in cell C1
copied the formula down so cell C10 is =(1/3)A10^3

this gives the resuls you stated....

what now?

do you want this to be automated at the click of a button?

let me know

Frazer
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frazer earned 50 total points
ID: 1610105
Hi,

I think this is what you are trying to do...

=(1/COLUMN(F4))*$A4^COLUMN(F4)

as long as you have numbers in column A this will give the intergral of that number in whichever column you copy the formula
e.g.
if you put the numbers 1-100 down column A, and copy the formula into cell C4, it would translate to
=(1/3)*$A4^3
this would give you the integral of 4 to the 3rd power

if you put it in cell G87, it would read
=(1/7)*A87^7
this would give you the integral of 87 to the 7th power

hope this helps

let me know

Frazer
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