I have written a code that will calculate the equation of the best fit-line for a given set of data-points.
The procedure is based on least square approximation, which, in simple words,works by finding a line that is at a minimum distance possible from all the points.
Let’s say you have the x-axis points stored in a matrix, ‘x’ & the y-axis points stored in a matrix ‘y’. Then the following code returns the value of the slope, ‘m’ and intercept ‘c’ of the best fit-line, and also the fitted points which are basically the points of the y-axis obtained from the equation of the best fit-line.
CODE:
//Linear Fit
//To fit a given set of data-points to a line.
//Written By: Manas Sharma(www.bragitoff.com)
funcprot(0);
function [f,m,c]=linefit(x,y)
n=size(x);
if n(2)
Sample Demo:
x=[1,2,3,4,5];
y=[2,4,6,8,10];
[yfit,m,c]=linefit(x,y)
Output:
c =
0.
m =
2.
yfit =
2.
4.
6.
8.
10.
In this example the y-axis points were simply twice of the value of x-axis points. Hence the equation of line, we get is y=mx+c=>y=2x.
Now let's try something not so straight forward.
Sample Demo:
x=[1,2,3,4,5];
y=[0.5,2.5,3.3,4.1,5.5];
[yfit,m,c]=linefit(x,y)
Output:
c =
- 0.3
m =
1.16
yfit =
0.86
2.02
3.18
4.34
5.5
We can now even plot the observed data-points and the fitted points(yfit) and compare the two.
plot2d(x,y,-5) //dotted points for the original/observed data-points
plot2d(x,yfit,5) //red line for the fitted points
Output:
I have created a module in SCILAB which contains the above macro, and once installed can be used as an in-built function. You can download it from here: https://atoms.scilab.org/toolboxes/curvefit
Leave your questions/suggestion/corrections in the comments section down below and I’ll get back to you soon.
[wpedon id="7041" align="center"]
Scilab says that there’s an error in the 3rd line. Some operator is missing. Idk…
I noticed that the if condition has gotten formatted wrongly due to some HTML problem.
Did you try changing this: “
” to this: “
if n(2)>n(1) then“.I have fixed the mistake now in the article.
Try this and let me know if it worked…
hi
x=[1,2,3,4,5];
–> y=[2,4,6,8,10];
–> [f,m,c]=linefit(x,y)
c =
Nan
m =
Nan
f =
Nan
i got this output …what could be the possible reason???
x= log(r)
x =
-Inf
1.0986123
2.0794415
2.5649494
2.8903718
3.1354942
3.3322045
3.4965076
3.6375862
3.7612001
3.871201
3.9702919
4.060443
4.1431347
4.2195077
How to sum this data? i want to use these for least square fitting.