dear Gnuplot users, I am using the following command to fit a set of data: f(x)=a*x+b; fit f(x) 'dataset' via a,b then I get the value of a and b with only one decimal digit like a=0.1, b=0.9 how can I get five decimal digits like a=0.00001, b=0.91112 ? Thanks

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7/8/2005 4:05:03 PM

David <dagao@exchange.uta.edu> wrote: > dear Gnuplot users, > I am using the following command to fit a set of data: > f(x)=a*x+b; > fit f(x) 'dataset' via a,b > then I get the value of a and b with only one decimal digit like a=0.1, > b=0.9 "get the value" --- where? All the outputs of 'fit' I'm aware of print with a good deal more than 1 significant digit. Well, unless all the others following it *are* exactly zero, that is. -- Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de) Even if all the snow were burnt, ashes would remain.

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7/8/2005 4:32:07 PM

Below is the copy: Final set of parameters Asymptotic Standard Error ======================= ========================== a = 0.0751221 +/- 0.005317 (7.078%) b = -29512.8 +/- 0.001603 (5.432e-06%) correlation matrix of the fit parameters: a b a 1.000 b -0.905 1.000 you can notice b= -29512.8 only has one decimal value. How to change it to have more than 1 decimal digit? Thanks

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7/8/2005 4:53:15 PM

David <dagao@exchange.uta.edu> wrote: > Below is the copy: > Final set of parameters Asymptotic Standard Error > ======================= ========================== > a = 0.0751221 +/- 0.005317 (7.078%) > b = -29512.8 +/- 0.001603 (5.432e-06%) > correlation matrix of the fit parameters: > a b > a 1.000 > b -0.905 1.000 > you can notice b= -29512.8 only has one decimal value. Actually the printed value has 6 significant digits. If that's not enough, just do a print b after completing the fit, and it'll show you more digits than you can use. -- Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de) Even if all the snow were burnt, ashes would remain.

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7/8/2005 5:14:44 PM

Thanks a lot ! Hans-Bernhard Broeker wrote: > David <dagao@exchange.uta.edu> wrote: > > Below is the copy: > > Final set of parameters Asymptotic Standard Error > > ======================= ========================== > > > a = 0.0751221 +/- 0.005317 (7.078%) > > b = -29512.8 +/- 0.001603 (5.432e-06%) > > > > correlation matrix of the fit parameters: > > > a b > > a 1.000 > > b -0.905 1.000 > > > you can notice b= -29512.8 only has one decimal value. > > Actually the printed value has 6 significant digits. If that's not > enough, just do a > > print b > > after completing the fit, and it'll show you more digits than you can > use. > > -- > Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de) > Even if all the snow were burnt, ashes would remain.

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7/8/2005 6:04:06 PM

Thanks. I checked help fit, it said it is using Marquardt-Levenberg algorithm. Could you please tell me the reference paper for the Marquardt-Levenberg algorithm ? Thanks again. Hans-Bernhard Broeker wrote: > David <dagao@exchange.uta.edu> wrote: > > Below is the copy: > > Final set of parameters Asymptotic Standard Error > > ======================= ========================== > > > a = 0.0751221 +/- 0.005317 (7.078%) > > b = -29512.8 +/- 0.001603 (5.432e-06%) > > > > correlation matrix of the fit parameters: > > > a b > > a 1.000 > > b -0.905 1.000 > > > you can notice b= -29512.8 only has one decimal value. > > Actually the printed value has 6 significant digits. If that's not > enough, just do a > > print b > > after completing the fit, and it'll show you more digits than you can > use. > > -- > Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de) > Even if all the snow were burnt, ashes would remain.

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7/8/2005 6:08:42 PM

David <dagao@exchange.uta.edu> wrote: > Could you please tell me the reference paper for the > Marquardt-Levenberg algorithm ? K. Levenberg. A Method for the Solution of Certain Non-linear Problems in Least Squares. Quarterly of Applied Mathematics, 2(2):164-168, Jul 1944 Marquardt, D.W.: An algorithm for least-squares estimation of nonlinear parameters, SIAM Journal of Applied Mathematics 11(2):431-441, Jun 1963 OTOH, any decent textbook on numerical maths should have an explanation of this algorithm for you. My actual reference for the implementation was not the paper, but H.R.Schwarz' textbook on numerical maths (in German). -- Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de) Even if all the snow were burnt, ashes would remain.

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7/10/2005 2:07:21 PM

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I have the following data file: http://www.cs.kuleuven.ac.be/~bartv/gnuplot/sobol.dat Now I want to do a least square fit on the data of the first and second column. The data in the first-column represent the x-values, the data in the second column represent the y-values. I don't need the rest of the columns. Now I now that x and y are related somehow as: y = a/(x**b) and I want to find a and b as accurate as possible. The file that plots my data to an .eps file is at http://www.cs.kuleuven.ac.be/~bartv/gnuplot/relative_error.pl If I don't specify an initial value for b_sob, the fit fails. If I do specify a starting value of 0.9 the fit works, but the result is not satisfying as can be seen from the .eps file at http://www.cs.kuleuven.ac.be/~bartv/gnuplot/relative_error.eps I have also tried to fit on log($2)=a-b*log($1) and then plot exp(a)/(x**b) but this didn't give me satisfying results either. How can I increase the quality of my fit? Regards, Bart -- "Share what you know. Learn what you don't." Bart Vandewoestyne wrote: > I have the following data file: > > http://www.cs.kuleuven.ac.be/~bartv/gnuplot/sobol.dat > > Now I want to do a least square fit on the data of the first and > second column. The data in the first-column represent the x-values, the > data in the second column represent the y-values. I don't need the rest > of the columns. > &...

Hi I have many file with extension (.dat). I need to open them in IDL and have least square fit. Is any one have idea on who to that. omerphysics@gmail.com writes: > I have many file with extension (.dat). I need to open them in IDL and > have least square fit. > Is any one have idea on who to that. Well, rest assured, the code will be less than 10 lines long. But, *which* 10 lines will depend on more details. What do you know about this problem? You can find a lot of hints at the web page below. Cheers, David -- David Fanning, Ph.D. Fanning Software Consulting, Inc. Coyote'...

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I'm trying to solve a system of 5+ equations for 3 unknowns, preferably using the least-squares method. I've Solve[] will not return solutions for more equations than you have unknowns. Fit[] does not work because my equations have 4 sets of data. Si=a*Ui + b*Vi + c*Wi, where i goes from 1 to 5 U, V, and W all come from a table, and S is from experimental data. I need to know how to solve for a,b,c given more than 3 equations. Background: The problem is actually trying to solve for Judd-Ofelt parameters of a laser crystal. S is the experimental line strength and U, V...

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Hi, I have equation: X=a_1*Y_1+a_2*Y_2+a_3*Y_3... where size(Y_n)=size(X)=[100 100] and size(a_n)=[1 1] X and Y_n are constants How can I do some kind of least squares fit to determine a_n? -Jonne Jonne wrote: > > > Hi, > > I have equation: > > X=a_1*Y_1+a_2*Y_2+a_3*Y_3... > > where size(Y_n)=size(X)=[100 100] and size(a_n)=[1 1] > X and Y_n are constants > > How can I do some kind of least squares fit to determine a_n? > > -Jonne A = [Y1(:),Y2(:),Y3(:)]\X(:); HTH, John ...

I need to find the coefficients k1-k6 of the following equation: P = G*(k1 + k2*T + k3*log(G) + k4*(log(G)).^2 + k5*T*log(G)+ k6*T*(log(G)).^2+k7*T.^2); The experimental data I have are P, G and T. Is there any MATLAB function in order to obtain the coefficients using least-squares fitting? Do I need the Curve Fitting Toolbox? Thank you very much, Zaira "Zaira " <Zaira.Girbau-Garcia@jrc.it> wrote in message <g0ccfp$jd9$1@fred.mathworks.com>... > I need to find the coefficients k1-k6 of the following equation: > > P = G*(k1 + k2*T + ...

Hello, i'm a student of University of Parma (Italy), and i've the following problem. I've found in internet the following model for fitting a plane from a cloud of point 3D. The link to the page is [ http://www.bmm.icnet.uk/people/suhail/plane.html ]. I've implemented this model in C++ and i've obtained some good result but when i try to reconstruct the passages of the procedure i'm not able to obtain the resulting matrix 3x3 denoted as W in the follow. I want to know if something one can help me to resolve this problem. I've tried to contact the author of the mod...

I am in need of some help. I am fitting Gaussian curves using the curve fitting toolbox. Once I fit the curve I get a x_0 centroid and a width. My goal is to fit the centroids of five different curves. I would like to fit the following and generate a slope and intercept. I am unable to do this is MATLAB. x y upper_y lower_y ..511 108 109.4 107.3 1.275 280 283 280 .... ..... ..... ..... .... ..... ..... so on and so ...

Hi everyone. A quick description of my problem: I have 4 sensor measurements (x_sensor), which can be estimated using a numerical model (nb the model is nonlinear is solved numerically...) I wish to fit the parameters of my model to best represent the measured data by performing a weighted least square fit with a different weighting for each sensor (due to different noise in the measurements). i.e. an objective function: error = A(x1_sensor - x1_model) + B(x2_sensor - x2_model) + C(x3_sensor - x3_model) + D(x4_sensor - x4_model) I am currently using lsqcurvefit but get a bad fit due to so...

I have a program that fits measured data to a function with a least squares fit. The measured data contains about 30 data points, and the fitting function has 5 parameters in total: y(x) = c1 * cos(c2*x + c3) * sin(c4*x)/x * exp(- c5*x) I also want to apply boundaries to the constants. I have tried several fitting algorithms, e.g. fminsearch and lsqnonlin. The trouble is, that since the fit is performed several thousands of times each time the program is executed, it is important that the function provides a fast fit. I have discovered that lsqnonlin is faster than fminsearch, but execution ...

Dear all, I'm a beginner of Matlab using. I have to find out how to fit a surface of 2 dimensional scatterd data in a least squares sense. Are there alreay toolboxes or functions to provide that? Can anybody help and give me more information? Thankx a lot Lukas Lukas wrote: > > > Dear all, > > I'm a beginner of Matlab using. > I have to find out how to fit a surface of 2 dimensional scatterd > data in a least squares sense. > > Are there alreay toolboxes or functions to provide that? > Can anybody help and give me more information? > > Thankx a l...

Hi all, I need some help with a curve fitting problem for data points. I have a set of data points g=[g1 g2 g3 g4 g5] h=[h1 h2 h3 h4 h5] and would like to fit these data to an equation y=ax/(b+x) in least square sense, with initial guesses a=170 and b = 1000 until R2 correlation is 95%. Thank you bubbub "Alison " <ucbeata@ucl.ac.uk> wrote in message <fhvlcg$d1g$1@fred.mathworks.com>... > Hi all, > > > I need some help with a curve fitting problem for data points. > > I have a set of data points > g=[g1 g2 g3 g4 g5] > h=[h1 h2 h3 h4 h...

Hi, Is there a way in Matlab to perform a least-squares fit on a column vector, with the constraint that the slope is zero? I have a column vector of periods extracted from an periodic waveform, and I'm trying to find the average period, where "average period" is defined as that period having the best least-squares fit. If I run p=polyfit(x,y,1), it will return a line having a slope (albeit a small slope). Anyway to do something similar but constrain the LSF operation that the slope must be zero? Thanks in advance On Thu, 2 Dec 2010 01:28:05 +0000 (UTC), "gkk gk...

Hi, I am trying to solve an optimization problem in Matlab. It is a nonlinear least squares problem. The goal is to derive the best-fit equations of seven straight lines (and other standard output e.g. residuals etc.). I've posted the problem description, and two images, one that describes the problem setting in detail, the other showing the set of 3D points I plotted for this, all here:: http://sites.google.com/site/niazarifin/matlab-project-images Since I never used any optimizer before, I'd truly appreciate if you can help on: 1.which Matlab function to use for the problem 2.what f...

Hi, I was wondering if it is possible to use lsqcurvefit to fit input data given multiple observables? That is, if I have two observables, y1 and y2, each effected differently by input variables x1, x2 and x3, can I use lsqcurvefit to obtain values for x1, x2, and x3? Thanks Ron Ron wrote: > > > Hi, > > I was wondering if it is possible to use lsqcurvefit to fit input > data given multiple observables? That is, if I have two > observables, > y1 and y2, each effected differently by input variables x1, x2 and > x3, can I use lsqcurvefit to obtain values for x1, x2, ...

Hi all, I'm new to Matlab I need to fit a surface to my observed data in order to find a polynomial equation of the surface. I have (x,y,z) data. Can anyone help me on this. Regards "Hashika " <hashikahimal@gmail.com> wrote in message <g5rn9d$kne$1@fred.mathworks.com>... > Hi all, > > I'm new to Matlab > > I need to fit a surface to my observed data in order to > find a polynomial equation of the surface. > > I have (x,y,z) data. > > Can anyone help me on this. > > Regards polyfitn, from the file exchange. http:/...

Hi I'm trying to write a program that takes data points and solves for coefficients for a least squares curve fit using matrices and starting from an initial condition. I tried building the coefficient matrix and solving for the coefficients but I end up with a straight line. Any advice would be appreciated. In article <eeed0b8.-1@webx.raydaftYaTP>, "John Roth" <jrothml@yahoo.com> writes: >Hi I'm trying to write a program that takes data points and solves >for coefficients for a least squares curve fit using matrices and which type of curve ? which type...

Iam using the lsqcurvefit function to estimate some parameters by fitting a kinetic model to experimental data.I need to get an estimate of the errors for the individual parameters that are calculated by the program.The function lsqcurvefit returns residuals but does not provide any estimates for the standard deviations for the parameters calculated.Iam sure there is a way of calculating them.Can someone please help? Thanks. Farah Bardai wrote: > > > Iam using the lsqcurvefit function to estimate some parameters by > fitting a kinetic model to experimental data.I need to get an &g...

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