how to do a TRENDLINE (polyfit?how?)

how can i do a trenline like this in matlab

http://i50.tinypic.com/nprtht.jpg

here is the data

http://www.speedyshare.com/ABueW/aaa.xlsx

thank you very much

Answer 1

[Matt Fig]

See the help for the POLYFIT function.

I see you edited the question to include (polyfit?how?) but what is the problem? Did you actually read the help for POLYFIT (that I even linked for you!) or do you want everyone else to do all the work for you?

If you have difficulty, why not show where you are stuck?

[joo]

i am sorry, when i edited i have not seen your answer. my probl in polyfit isthat i don't get a R2 like excel.

even if i do it in excel and then try thsat results in matlab i don't get a good answer

http://www.speedyshare.com/xGgTF/Nova-pasta.rar

can you help me?

[Matt Fig]

I downloaded your file and got the exact same results as Excel with MATLAB. I called the data N.

>> X = N(22:end,1);
>> Y = N(22:end,2);
>> [pp,s] = polyfit(X,Y,1)

pp =

     -0.0406    0.8654

s = 

          R: [2x2 double]
         df: 76
      normr: 0.2742

>> r_squared = 1 - s.normr^2 / norm(Y-mean(Y))^2

r_squared =

      0.9719

Answer 2

[Image Analyst]

There is a curve fitting toolbox if you want. It handles non-polynomial functions. Check it out.

[joo]

thank i checked. but there is only a possibility, to plot 'linear'. nothing more is possible right=?

[Image Analyst]

Not sure what you looked at but I saw all kinds of curvy and wavy functions being fitted to data.

[joo]

yes, i know. but what i need is the black straight line http://i50.tinypic.com/nprtht.jpg that in excel is a trendline as you can see in the excel file< http://www.speedyshare.com/ABueW/aaa.xlsx>. if you npl,ease could helop i would be very grateful. thank you