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In this example the proc density_function referenced by the 'function' attribute is implemented in the xml .spd file but it is very simple and only invokes another procedure named MyDensityFunction adding some arguments. The body of the tcl procedure could be implemented separatelly separately in a .tcl file (sourced in the problemtype), this facilitate its edition and debug.
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where scalar is a keyword,
interpolator_func is the same name used in <functionVariable n="interpolator_func" ...
x is the same variable name used in <functionVariable ... variable="x" ...
Temp is the magnitude accoding according to the units used in <functionVariable ... units="°C">
The graphical interface will show something like this
and pressing the rigth right button will open a window to edit the xy graph:
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