Tarsier Tools

Linear Interpolation Function - TT03-002
Designed for Microsoft Excel, this "Tarsier Tool" interpolates between consecutive ordered points from the given data. The function can be configured to interpolate using either a step or linear function. If the input value is outside of the range of the X coordinates the function can be configured to either perform a linear extrapolation using the two nearest points; return a constant value of the nearest value or return the Excel #N/A value.

Please note that this Tarsier tool is distributed with NO WARRANTY.

This page contains the following information on this Tarsier Tool.
Usage Instructions
License Fee
How to Install
How to Uninstall
Revision History
Software for Download
Source Code
Technical Support
Further Information

Usage Instructions
To use the Linear Interpolation Function:
The following instructions assume you know how to use Excel Functions.
If you use Excel's function paste menu, our interpolation function can be found either under the "All" listing or under "User defined".

The function has three mandatory arguments and two optional arguments.
You must;

1. specify the range of cells containing the known X values, (argument known_x)
2. specify the range of cells containing the known Y values, (argument known_y)
3. specify the X value you are interpolating against, (argument x_Value)

With this information the function will perform linear interpolation to find the specified value, or extrapolate to find the Y value if the X value is outside the range of known X values.

Additionally, you can specify the following options;

1. what value should be returned if the X value interpolated against is outside the range of known X values, (argument cutOffAction, 0 = extrapolate; 1 = cut off at the nearest known value, 2 = return #NUM!),
2. use step interpolation, (argument step binary value, false = perform linear interpolation, true = perform stepwise interpolation),

Important Note:
The known X values must be in numerical order, minimum to maximum.

Examples:
"Example Result" is calculated using the following data.

Description	x_value	cutOff	step	Example formula	Example result
Compulsory arguments - within X value range	1.5	Not specified	Not specified	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,1.5)	2.7
Compulsory arguments - outside X value range	-1.0	Not specified	Not specified	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,-1.0)	0.5
	6.0	Not specified	Not specified	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,6.0)	35.5
Cut off if outside X value range	-1.0	1	Not specified	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,-1.0,1)	0.8
	6.0	1	Not specified	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,6.0,1)	26.0
Return error if outside X value range	-1.0	2	Not specified	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,-1.0,2)	#NUM!
	6.0	2	Not specified	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,6.0,2)	#NUM!
Stepwise interpolation - within X value range	1.5	0, 1, 2	True	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,1.5,0,True)	1.1
	2.001	0, 1, 2	True	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,2.001,0,True)	4.3
	3.9999	0, 1, 2	True	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,3.9999,0,True)	9.9
Stepwise interpolation - outside X value range	-1.0	0	True	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,-1.0,0,True)	0.8
	6.0	1	True	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,6.0,1,True)	26
	-4	2	True	=LinearInterpolator($A$2:$A$7,$B$2:$B$7,-4.0,2,True)	#NUM!

Note, constant values shown in the example equations above can of course be replaced be replaced by cell references, definitions, etc...

Error Messages
When using the Linear Interpolation Function, it will return Excel error codes in the following circumstances;

1. If you only supply one point (one X and one Y value) the function will return the Excel #NUM! value,

License Fee
There is no license fee for personal use of this tool. However, if you are using this software within software that you are developing and intend to sell, please e-mail us for details of the license fee.

How to Install

1. Download the appropriate Linear Interpolation Function for your version of Windows® and Excel (see the Software section of this page) and use the save this file to disk option to save the file to a directory on your computer where you'll be able to find it later. (See Note below). A good location to save the file is to your Microsoft Excel Add-In directory, which can be found by completing steps 2, and 3.
2. Start Microsoft Excel, and from the Tools menu, select Add-Ins...,
3. Click on the Browse... button, which will list all the non Microsoft Excel Add-Ins,
4. A. If you saved the file to your Microsoft Excel Add-In directory, select TT03-002.xla from the list of files and click the OK button,
   B. If you saved the file to another directory, change to that directory in the same way that you would use the Open file dialog to open a file; then select TT03-002.xla from the list of files and click the OK button,
   
5. Ensure that the box for the "Linear Interpolator" is ticked/checked, as shown below, and click OK
   

Our Linear Interpolator Function is now ready for use.

Note E-mail us if you would like us to send you this Tarsier Tool directly, rather than download it from the internet. Please ensure that you state that you want our Linear Interpolator Function, (TT03-002) somewhere in your e-mail.

How to Un-install
To uninstall the Linear Interpolator Function,

1. Start Microsoft Excel, and from the Tools menu, select Add-Ins...,
2. Un-tick/un-check the box for the "Linear Interpolator Function" and click OK.

If you decide that you want to use the Linear Interpolator Function again, just perform steps 2 and 5 from the How to Install Procedure.)

If you want to remove the Linear Interpolator Function reference from the list of Add-Ins,

1. Delete the file TT03-002.xla from your computer,
2. Start Microsoft Excel, and from the Tools menu, select Add-Ins...,
3. Try to tick/check the box for the "Linear Interpolator Function" the following message will appear, "Cannot find add in 'directory path\TT03-002.xla'. Delete from list?". Click Yes,
4. Close the Add-In dialog box by clicking OK.

Revision History

Rev	Date	Description
1.0	10-Nov-03	Initial Version Released

Software for Download

Windows Ver.	Excel Ver.	Software
Win 2000	Excel 97	TT03-002.xla
Win XP Pro	Excel 2003

Please let us know if you have used our Linear Interpolation Function, successfully or not, on any other Windows® and Excel combination.

Source Code
In accordance with the GNU General Public License the Microsoft Excel Add-in used to distribute this Tarsier Tool is not password protected allowing you to view and modify it if you require. You should review the GNU GPL to determine your rights to distribute this software and be informed that this software is distributebuted with NO WARRANTY.

Technical Support
Frequently Asked Questions
Currently there are no FAQ for this tool.
If you have a question, please e-mail it to us. Please ensure that you identify which Tarsier Tool, (Linear Interpolation Function TT03-002) the question is about.

Bug-Reports
Currently there are no reported bugs for this tool.
If you suspect a bug in this Tarsier Tool, before contacting us, please check the FAQs and Bug Reports to see if it has already been idento see if it has already been identified.
If it hasn't, e-mail a description to us. Please ensure you identify the software (Linear Interpolation Function TT03-002) somewhere in the e-mail and include as much detail as possible; including a simple example application is always helpful! but make sure it does not contain proprietary or confidential information.

Further Information
This section will be updated with links to information relating to the principles behind and the uses of this Tarsier Tool, as we become aware of them.