2D-Linear Fit needed

Hello,
I have to find the best straight line in a x-y measurement array.
The "Linear Fit.vi" uses a linear regression method normal to the x-Axes which leads to bad results if the sollution would be near a vertical straight line.
e.g.: with a Pair of measurement points with:
1.: x=0 Y=+1
2.: x=0 Y=-1
I would like to get a straigth vertical line (x=0, k=inf or something which represents this), the Linear Fit.vi's result is NaN
Does someone know where to find a vi for this?
Thank you for any comments.
Greetings
Mario Hirth

Mario Hirth wrote:
Since I use the residuum of the linear fitting to evaluate the measurement (which should represent a straight line, but I dont know in which direction), I have to be mathematically correct.
I also had a solution by iteration with: "find slope" => "turn measurement data into x-axis according to slope" => start again with finding slope => do this about 5 times etc...
in principle this works, but since I have to make a iteration with the result of this output (which is a different story), I have a iterationtask inside an iteration task.
It works, but its neither a beatiful sollution nor a quick (means CPU-intensive).
Mathematically, this makes no sense to me. Can you explain what it is supposed to achieve?
What is the error in x and y for each data point?
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How to use linear fit

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Brein wrote:
This is my vi. I am using labview 7.0 and vision 7.0. This project is about finding a relationship between concentration of a certain solution and its color value using rgb space. I am already able to plot the relation ship found in sequence structure 3 of 3(assuming the first sequence is 0 of 3). How to put a linear fit in my data points?
So you need to do a global fit to three datasets (R, G, & B). Since you seem to deal with a greyscale image, it is probably sufficient to fit only a single channel. What function do you use in excel?
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Linear Fit errors

I am trying to make use of the "Linear Fit" and "Linear Fit Coefficients" vi's, but I am getting errors despite inputting what I thought was correct. If I connect my two 1D data arrays to the 'X' and 'Y' input terminals then I get the error -20002. If I connect empty arrays, I get the error -20006. I'm leaving all the other inputs unconnected.
In looking for a solution to this, I came across something altenbach said a few years ago:
altenbach wrote:
Some possible errors that can occur with linear fit (but they would generated different error codes):
You have only a two-column file. In this case you need columns 0 and 1 (column 2 does not exists) error -20002
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I only half-understand what he meant, and/or how it would apply to what I'm doing wrong. Can anyone help me out here?
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Go to Solution.

Please attach code.
-20002 states that the input sequences must be the same size. So X and Y need to be the same length. Verify this first.
-20006 states that the input lengths must be at least 2 elements. So passing in empty arrays makes perfect sense here.
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Linear fit without professional version. Workarounds anyone?

Hey, I'm trying to do some analysis and need to find the slope of a curve. The drivers I have are trying to access the linear fit function but I don't have the pro version so I can't use it. Anyone know of a free workaround VI possibly or any other solution?
Thanks

Hi acolbourn
The linear fit just implements the least squares algorithm, this is pretty simple.
You can read how this algorithm works here:
http://en.wikipedia.org/wiki/Least_squares
What parameters does the driver call the function with just X and Y as input, and best fit as output?
Regards,
Anders Rohde

Linear Fits

I have some data that should follow a straight line, but there are spikes in
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Craig Graham
Physicist/Labview Programmer
Lancaster University, UK

I have a question about your approach:
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Attachments:
Rawsignal test.vi ‏245 KB
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Hi maurlind,
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Follow my VI.
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phanikiran wrote:
Hi koen,
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Go to Solution.

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LabVIEW Champion . Do more with less code and in less time .

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Message Edited by Eirikur on 01-09-2008 01:25 PM
Regards,
Eirikur Runarsson
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NI Denmark

2D-Linear Fit needed

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