Variable-Length dependent formula

[chris_manning]

Hi all-

I have a specific (and I believe, difficult problem) I have an Excel
program that does several calculations on a data set that is an input
from another program.

Background: The basic gist is that I have a program that varies voltage
sequentially and measures the corresponding current. The program then
outputs these points in a text file seperated by commas. The user then
copies this information into the Excel sheet and runs a macro in order
to do all the calculations on the function.

Problem: Previously, all files were in the same format: for example, it
swept the voltage from 0V to 0.8V at 100 V/s, giving 800 data points per
segment. However, now, some of the data is different (0V to 1.6V sweeps
at perhaps 10 V/s, for example, giving 160 Data points per segment). My
last problem (there is a cut-and-paste part of the macro that I have
figured out how to cut-and-paste variable lengths based upon user input
of V/s and Voltage range) is that I have a portion of the program that
uses a simple formula for mathematically calculating the integral of
the 'function' that is represented by the data points:

(T2-T1)*X1+.5((X2-X1)*(T2-T1))+(The contents of the previous cell)

The problem is that this method relies on there only being a certain
amount of data points. Is there a way to adjust it for variable
length?

 

[MrShorty]

Your choice of Riemann sum to approximate the integral is genera
enough for any number of intervals. It's called the trapezoidal rul
and the formula can be simplified to sum(1/2*(T2-T1)*(X1+X2)). It'
general enough to work, so something in the way you are applying i
isn't allowing you to be general enough. How are you putting thi
formula into the spreadsheet? All you really should have to do i
extend that formula down the column until it covers the entire dat
set. Without knowing how you are putting the formula into th
spreadsheet, I'm not sure how best to suggest that you extend tha
procedure

 

[B. R.Ramachandran]

Hi,

Your formula is analogous to (T2-T1)*(X1+X2)/2 as MrShorty puts it.
If you are entering this formula in the Excel spreadsheet, you have to drag
down the formula all the way to the last row containing data (a shortcut is,
click on the cell containing your formula, move the cursor-pointer to the
bottom right corner -the cursor changes into a skinny plus sign - and
double-click; the column would automatically fill down).

Regards
B.R.Ramachandran