When you have completed the setup of your fitting problem, you can click the Run fitting ... menu item in the Automatic Fitting menu to begin the fitting calculation.
Run fitting ...
Ansys Polymat will automatically compute curves corresponding to all of the specified experimental data curves. When the automatic fitting calculation is complete, Ansys Polymat will save the results to the file you specified in Specifying a Name for the Material Data File. When the calculation is complete, Ansys Polymat will automatically update the chart with the computed curve(s) and the experimental curve(s). The steady shear viscosity, storage and loss moduli, and the rest normal stress difference will be plotted on the same log-log graph. A second plot will display the extensional viscosity curve(s), using a logarithmic scale on the Y axis (to represent the viscosity) and a linear scale on the X axis (to represent time). See The Curve Settings for information about changing the appearance of the curves.
If you do not want Ansys Polymat to update the curves in the chart automatically, click Do not update graphics after each run in the Automatic Fitting menu before you run the fitting calculation.
If you want to plot curves other than those that were directly calculated, you can read the material data file into Ansys Polymat and use the menu button near the top of the Ansys Polymat application window to specify additional curves to be plotted. (See Specifying the Curves to be Calculated for details, then use the menu button to update the chart.
In an automatic fitting for a viscoelastic model, steady shear viscosity, storage modulus, and loss modulus are the mandatory curves whereas, first normal stress difference and extensional viscosity are the optional curves. For a generalized Newtonian model, the steady shear viscosity is a mandatory curve. After an automatic fitting, it is possible to pursue fitting, if necessary.
Select the Pursue fitting ... menu item in the Automatic Fitting menu.
Pursue fitting ...
This option is available after at least one fitting. Fitting is continued with the values of the parameters of the initialized model using the values obtained at the previous fitting step. The fixed parameters will not change. You do not have to change any flag associated to the parameter in Material data menus, Ansys Polymat automatically makes these changes.
You can check how the fitting has been performed using the View listing of fitting menu.
View listing of fitting
When you click the View listing of fitting option, a new window appears, presenting a summary of the last fitting run.
Calculations are stopped when the maximum number of iterations is reached, or if the following distances are adequately reduced:
The distance between two successive solutions.
The distances between the solution and the experimental points.
Given the assumption that a fluid model has n parameters to fit:
 | (5–2) |
If you compare the value of these parameters for two successive iterations i and i+1, respectfully:
 | (5–3) |
 | (5–4) |
The distance 
for parameter j becomes:
 | (5–5) |
when 
, the global distance D is calculated
as:
 | (5–6) |
Here, assume that you are comparing a single experimental curve to its modelized curve, at iteration i.
The experimental curve is composed of a set of P points:
 | (5–7) |
If 
is the shear rate and if the shear rate range is defined
as 
, the subset of points having 
in that interval is taken.
At iteration i, you can evaluate the modelized curve knowing the value of the parameters at that iteration:
 | (5–8) |
For the set of abscissas 
, the modelized curve is composed of a set of
P points:
 | (5–9) |
The distance for point j can be defined as:
 | (5–10) |
such that
 | (5–11) |
Note that when there are several experimental curves, the distance printed in the listing will be the sum of the distances of each curve.