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ezfit
Fit data with arbitrary fitting function

Description ```ezfit(FUN) fits the active curve with the function FUN. See below for the syntax of FUN. If FUN is not specified, 'linear' is used. By default, the first curve in the active figure is fitted - see fitparam to change this default behavior. To fit another curve, select it before calling ezfit. If some data are selected by the "Data Brushing" tool (only for Matlab >= 7.6), only those data are fitted. ezfit(X,Y,FUN) or ezfit(Y,FUN) fits the data (X,Y) (or Y) using the function FUN. X and Y must be vectors of equal length. If X is not specified, X=[1, 2, 3...] is assumed. ezfit(X,Y,FUN), where X is a 1-by-N vector and Y is a 2-by-N matrix, also specifies the weights for Y(2,:) (error bars). By default, when Y is a 1-by-N vector, all the weights are 1. Note that ezfit only computes the coefficients, but does not display the fit. Use showfit to display the fit. The function string FUN can be: - the name of a predefined fitting function (see below). - the name of a user-defined fitting function (see editfit). - an equation, in the form 'y(x)=...', where 'x' represents the X-data, and all the other variables are parameters to be fitted ('a', 'x_0', 'tau', ...). Example: 'y(x)=a*sin(b*x)'. If the left-hand-side 'y(x)' is not specified, 'x' is taken for the X-Data. All the parameter names are accepted, except Matlab reserved strings ('sin', 'pi', ...) The predefined fitting functions are: - linear y = m * x - affine or poly1 y = a*x + b - poly{n} y = a0 + a1 * x + ... + an * x^n - power y = c*x^n - sin y = a * sin (b * x) - cos y = a * cos (b * x) - exp y = a * exp (b * x) - log y = a * log (b * x) - cngauss y = exp(-x^2/(2*s^2))/(2*pi*s^2)^(1/2) - cfgauss y = a*exp(-x^2/(2*s^2)) - ngauss y = exp(-(x-x0)^2/(2*s^2))/(2*pi*s^2)^(1/2) - gauss y = a*exp(-(x-x0)^2/(2*s^2)) 'ngauss' is a 2-parameters normalized Gaussian, and 'gauss' is a 3-parameters non-normalized (free) Gaussian. 'cngauss' and 'cfgauss' are centered normalized and centered free Gaussian, respectively. ezfit is based on Matlab's built-in FMINSEARCH function (Nelder-Mead method), which performs an unconstrained nonlinear minimization of the SSR (sum of squared residuals) with respect to the various parameters. The correlation coefficient R is defined as SSreg / SStot, where SSreg = sum ((y_fit - mean(y)).^2) % regression sum of squares SStot = sum ((y - mean(y)).^2) % total sum of squares (see https://en.wikipedia.org/wiki/Pearson_product-moment_correlation_coefficient) (NB: definition of R changed in Ezyfit v2.44) Nonlinear minimization requires starting guesses (or starting estimates) for the fit parameters. By default, all the starting guesses are taken as 1, or, when using predefined fits (e.g., exp, gauss, power...), the starting guesses are determined depending on the range of the data to be fitted. However, in most cases, values closer to the expected result should be specified to "help" the convergence. It is sufficient to choose values that have the correct sign and correct order of magnitude, e.g. 0.01, 1, 100... The starting guesses for the parameters may be specified in two ways: - directly in the string FUN, after the fit definition: 'c0 + a*sin(pi*x/lambda); c0=1; a=0.1; lambda=100' ('!' or '\$' may also be used instead of ';'). - by specifying them as an additional input argument for ezfit: ezfit(x,y,'c0 + a*sin(pi*x/lambda)',[0.1 1 100]); Note that in this case the parameters must be ordered alphabetically. Note that if both methods are used, only the starting guesses given in the string FUN are considered. By default, Y is fitted in linear mode. If you want to fit LOG(Y) instead, you must specify the option 'log' to the string FUN, separated by the symbol ';' or '\$' or '!' (eg, FUN='a*x^n;log'). This is specially useful to fit power laws with equally weighted points in a log scale. If nothing specified, the option 'lin' is used. Example plotsample('power') and compare the results of: ezfit('power;lin') ezfit('power;log') F = ezfit(...) also returns a structure F having the following fields: - name name of the fit - eq equation of the fit - param cell array of strings: names of the parameters - m values of the coefficients - m0 initial guess for the coefficients - r correlation coefficient R (Pearson's correlation) - fitmode 'lin' (y is fitted) or 'log' (log(y) is fitted) mode This structure F can be further used with showfit, dispeqfit, showeqbox, makevarfit and editcoeff. From F, you can get the values of the fitted parameters. If you want to create in the current Matlab workspace the variables associated to these parameters, use makevarfit (or set the option 'automakevarfit' to 'on' in fitparam). Examples plotsample damposc f = ezfit('u(t) = c + u_a * sin(2*pi*t/T) * exp(-t/tau); T=5; tau=20'); showfit(f); plotsample poly2 [x,y] = pickdata; f = ezfit(x, y, 'z(v) = poly3'); editcoeff(f); plotsample poly2 f = ezfit('beta(z) = poly2'); showfit(f, 'fitcolor', 'red', 'fitlinewidth', 2); See Also showfit, plotsample, dispeqfit, editcoeff, FMINSEARCH, makevarfit, fitparam. Published output in the Help browser showdemo ezfit ```
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