Autocorrelation Function

So I've got some data, which has the approximate form of a sine function. I want to find all the x-axis intercepts. I tried using the intercept function and swapping around the y values for the x values, but it only returns 1 value (so I'd guess it uses a linear regression to estimate a single line through the axis).

I was thinking of trying a nested if/and statement but I haven't quite figured out how to do it. Basically I want to identify the two values where it switches from positive to negative and also indentify the values where it goes negative to positive, I can then fit a straight line between them to find a better approximation of the intercept (though it might not be necessary). Preferably I'd like it all one function as I'm not doing it in VBA (I might do later though, we'll see).

Can anyone suggest how I'd find these value or the x-intercept. Any help would be greatly appreciated.

Is there an Excel guru that can help with this - its related to "drop down menus"


I have 2 colombs of data.

AT the bottom of the first, I have created a drop down menu using the "data validation" feature in excel.

At the bottom of the second colomb, I have used an "IF" function that returns a result, which depends on what value is chosen from the drop down menu in colomb 1

The problem I have is that I want the TRUE result from the IF function to be another drop down menu, being the data in colomb 2.


How do you write an IF function where the TRUE result is a drop down menu??
I tried to create a drop down menu of colomb2 elsewhere in the spread sheet, and used that cells location as the TRUE value, but this didn't work either...

ANy suggestions??

I am trying to work out how to calculate the geometric mean of a series of values, some of which are negative, ie. investment returns over a series of years with some negatives.

The Geomean function doesn't work because it only uses positive numbers.

Any help would be greatly appreciated.

Hello,

I have two columns of data: column A contains the date and time in the form dd/mm/yyyy. Column B contains a number value. All the times are in order, so column A looks like:

01/01/2007
02/01/2007
03/01/2007

I have data from 2007 to 2010. I need to calculate an average daily value (in column B) for each month, and display it in column C. So, for January, I need to calculate the average of 31 days, February, 28 days, etc.

Is there a function I can use to do this? I've been trying the AVERAGEIF formula but can't get it to work. Any ideas would be much appreciated!

Many thanks,
Caitlin

Need a formula to calculate weeks stock in hand based on 12 months forecast.

Here is the example.

Jan2011 Feb2011 Mar2011 Apr2011 May2011 Jun2011 Jul2011 Aug2011 Sep2011 Oct2011 Nov2011 Dec2011 ----------- ----------- ----------- ----------- ----------- ----------- ----------- ----------- ----------- ----------- ----------- ----------- Product XXXXX Actual/Forecast : 174 1674 574 574 524 524 524 524 524 728 728 728 New Purchases : 0 0 0 0 1002 0 0 0 0 0 0 0 Goods In Transit: 0 1506 0 0 0 0 0 0 0 0 0 0 Other Movements : 0 0 0 0 0 0 0 0 0 0 0 0 Closing Stock : 1270 1102 528 -46 432 -92 -616 -1140 -1664 -2392 -3120 -3848 Week Stock in Hand ? ? ? ? ? ? ? ? ? ? ? ?

So, in Month of Jan2011 the Closing stock is 1270, need a formula to calculate how many weeks will this stock cover look at future forecast.