forked from IPKM/nmreval
43 lines
2.3 KiB
ReStructuredText
43 lines
2.3 KiB
ReStructuredText
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.. _user_guide.fit:
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============
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Fitting data
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============
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.. image:: ../_static/fit_dialog.png
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:scale: 80%
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:align: center
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The picture gives an example of dialog to setup and start fits.
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First, there is the possibiity to fit different functions, called models to differentiate from the functions inside each
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model, to different data simultaneously.
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In the given example, two models were would be used during fit:
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test1 and test3 use the default model, in this case model a,
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while test2 uses model b.
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In the middle column, the functions of model a are currently given in a tree structure:
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It is comprised of three functions: a constant, a sine curve, which is a child of the constant, and free diffusion.
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Functions can be dragged by mouse to each position, including a child position, and it is possible to switch between the
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four basic arithmetic operations (+, -, \*, /) by striking the corresponding key.
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Function at the same level, e.g., constant and free diffusion, are evaluated in the given order.
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Children of a function take precedence over the following functions.
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This means for the given example, that model a is something like
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.. math::
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f(x) = [\text{constant} / \text{sine}] + \text{diffusion}
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It is possible to skip functions by de-selecting it.
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This choice alse affects children, even if they are selected.
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The right column gives access to the parameter of selected function, in this case of the free diffusion function.
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Here, the parameter :math:`M_0` is linked to the parameter :math:`C` of another constant function of model b
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(identifiable by the number behind the name).
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Linkage links not only parameter between function but all settings, e.g., if :math:`C` is fixed, :math:`M_0` is fixed.
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Some parameters like gradient :math:`g` are predefined as fixed parameters and are lacking any options besides their value.
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Upper and lower bounds may be given.
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If one or two of the bounds are not given, this parameter is unbounded on the respective side.
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If a parameter has one entry, this value is initial parameter for all data sets.
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If the number of entries is greater than the number of data sets, the first :math:`n` values are used.
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Here, test1 uses 1 as parameter for :math:`t_{ev}` and test3 uses 3.
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If the number of entries is less than the number of data sets, the last value will be used for each additional set.
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