![]() # add one Gaussian to each guess Gaussian # search for the peak in the whole guess Gaussian # the same, but name the new function guess %f1 = Gaussian # add Gaussian in the given guess Gaussian Substitutions must be assigned in the same line, after the keyword where. There is a simple substitution mechanism that makes writing complicated X < center ? Lorentzian(height, center, hwhm1) # split-Gaussian, the same as built-in SplitGaussian (should be in one line)ĭefine SplitG(height, center, hwhm1=fwhm*0.5, hwhm2=fwhm*0.5) = PseudoVoigt (should be in one line)ĭefine GLSum(height, center, hwhm, shape) = Gaussian(height*(1-shape), center, hwhm) # area-based Gaussian can be defined as modification of built-in Gaussian # (it is the same as built-in GaussianA function)ĭefine GaussianArea(area, center, hwhm) = Gaussian(area/hwhm/sqrt(pi/ln(2)), center, hwhm) ![]() # supersonic beam arrival time distributionĭefine SuBeArTiDi(c, s, v0, dv) = c*(s/x)^3*exp(-(((s/x)-v0)/dv)^2)/x # this is how some built-in functions could be definedĭefine MyLorentzian(height, center, hwhm) = height/(1+((x-center)/hwhm)^2)ĭefine M圜ubic(a0=height,a1=0, a2=0, a3=0) = a0 + a1*x + a2*x^2 + a3*x^3 Hopefully the examples can make the syntax clear: When giving a full formula, the right-hand side of the equality sign X < expression ? Function1(…) : Function2(…) as a re-parametrization of existing function.by giving a full formula, like in the example above,.The default value always binds a simple-variable to the parameter. The default value can be either a number or an expression that depends hwhm means half width at half maximum,Įach parameter may have a default value (see the examples below). The initial values of these parameters can be guessed (command guess)įrom the data. if the functions is S-shaped (sigmoidal) or step-like:.if the functions is peak-like (bell-shaped):.There are special names of parameters that Fityk understands: Just use it on the right-hand side of the definition. ![]() The name “x” is reserved, do not put it into parameter list, Parameter name must start with lowercase letter and,Ĭontain only lowercase letters, digits and the underscore (‘_’). The name of the type is followed by parameters in brackets. The name of new type must start with an upper-case letter,Ĭontain only letters and digits and have at least two characters. In Fityk, this part of the model is called x-correction.ĭefine MyGaussian(height, center, hwhm) = height*exp(-ln(2)*((x-center)/hwhm)^2) If this is the case, such errors should be a part of the model. Zero shift or, in powder diffraction measurements,īy displacement of sample in the instrument. In experiments we often have the situation that the measured x valuesĪre subject to systematic errors caused, for example, by instrumental The parameters will be fitted to achieve agreement To a component function, not when when referring to the sum (model), To avoid confusion, the name function will be used only when referring This is not a limitation, because the user can add any function The model F is constructed as a list of component functionsĮach component function is one of predefined functions, This chapter shows how to construct the model.Ĭomplex models are often a sum of many functions. Underlying idea of what that function should look like. Modeling canĪlso be used as a kind of constrained interpolation, where you want toĮxtend a few data points into a continuous function, but with some ![]() Other times, the model’s parameters comeįrom some underlying theory that the data are supposed to satisfy Įxamples are coefficients of rate equations in a complex network ofĬhemical reactions, or orbital elements of a binary star. Sometimes the model is simply a convenient class ofįunctions, such as polynomials or Gaussians, and the fit supplies theĪppropriate coefficients. The data by fitting it to a “model” that depends on adjustable Given a set of observations, one often wants to condense and summarize > To unsubscribe from this group and stop receiving emails from it, send an email to To view this discussion on the web visit. > You received this message because you are subscribed to the Google Groups "fityk-users" group. > Could you be more specific? What exactly means that it works not so well? > I have doubts about calculating the area under the curve of my dataset in certain ranges. > On Wed, at 4:54 PM Marcin Wojdyr wrote: The number I obtain from the peak at the right of 550 nm is roughly the same as the peak at the left of 600, (10.3731 and 14.643 respectively), when I was expecting at least three times larger.
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