# forum.alglib.net

ALGLIB forum
 It is currently Sat Jul 20, 2024 12:25 pm

 All times are UTC

### Forum rules

1. This forum can be used for discussion of both ALGLIB-related and general numerical analysis questions
2. This forum is English-only - postings in other languages will be removed.

 Page 1 of 1 [ 1 post ]
 Print view Previous topic | Next topic
Author Message
 Post subject: Help needed with polynomialfitPosted: Thu May 26, 2011 6:21 pm

Joined: Thu May 26, 2011 6:15 pm
Posts: 1
Hi there

Very nice work on this package!

I am trying to make a straight line fitting (a*x + b) on some data-points I have, but I am having some problems obtaining similar results using alglib.net as I get with Excel. This is my code:
Code:
double[] x = new double[] { -13,-12,-11,-10,-9,-8,-7,-6,-5,-4,-3,-2,-1,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,160,17 };
double[] y = new double[] { 3.94117647058823, 3.72727272727272,2.8695652173913,3.34482758620689,3.06896551724137,3.66666666666666,2.92307692307692,3.03030303030303,2.93333333333333,2.60344827586206,2.71111111111111,2,2.14084507042253,2.25757575757575,2.5,1.95121951219512,2.22807017543859,1.98630136986301,1.94520547945205,1.7012987012987,1.68055555555555,1.86301369863013,1.56060606060606,1.4,1.61538461538461,1.37254901960784,1.41176470588235,1.38095238095238,1.45,1.33333333333333,1.378378378378 };
int m = 2;
double t = 2;
int info;
alglib.barycentricinterpolant p;
alglib.polynomialfitreport rep;
double v;
alglib.polynomialfit(x, y, m, out info, out p, out rep);
v = alglib.barycentriccalc(p, t);
double[] a2;
alglib.polynomialbar2pow(p, out a2);

The result is this:

[0] 2.3410245814871029 double
[1] -0.012596899769274472 double (a*x + b)

Which translates to:
-0.012596899769274472x + 2.3410245814871029

But using the same samples in excel I archive the following numbers:
-0.0814x + 2.42

What am I doing wrong here?
Thanks

Top

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 1 [ 1 post ]

 All times are UTC

#### Who is online

Users browsing this forum: No registered users and 2 guests

 You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum

Search for: