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