Analysing Monte-Carlo Results

In this topic:


Plots of Monte Carlo analyses are performed in exactly the same manner as for normal runs. When you probe a circuit point, curves for each run in the MC analysis will be created.

In common with other multi-step analyses, the curves generated for multi-step Monte Carlo are grouped and operations performed on them treat the group as a single entity. You can break the group using menu Curves > Ungroup Selected Curves.

Identifying Curves

Sometimes it is useful to know exactly which run a particular curve is associated with. To do this, move the cursor so that it is on a curve of interest. The selection cursor (small square box) should locate itself on the curve. In the status box at the bottom of the graph window, you should see a label in the form Run=nnn (division=ddd) where nnn and ddd are integers. (ddd is always 1 less than nnn). The run number can be cross-referenced with the entry in the log file to find information about the run that created the curve. You can also obtain the seed value used so that the run can be repeated. See Setting the Seed Value and Log File for more details.

Plotting a single Curve

If you wish to plot a single curve in a Monte Carlo set, you must obtain the division number (always 1 less than the run number) then use the Probe > Add Curve... menu to plot an indexed expression. We use an example to explain the process.

Using the Chebyshev filter example, let's suppose that we wish to plot the curve of the filter output created by run 49 (division 48) alone without the remaining curves. Proceed as follows.

  1. Run the chebyshev filter example as explained at the beginning of this chapter.
  2. Select menu Probe > Add Curve...
  3. Click on the output of the filter. You should see C4_P entered in the Y expression box.
  4. You must now modify the expression you have entered to give it an index value. For the simple case of a single voltage or current just append it with

    where division-index is the run number less 1. In this example the run number is 49 so we enter 48 for the index. You should now have:
    displayed in the Y expression box.
  5. Close box. You should see a single curve plotted.
An alternative method of plotting single curves is given in Setting the Seed Value.

Creating Histograms

See Performance Analysis and Histograms.

Log File

Multi-step Monte Carlo analyses generate a log file that documents the values of all toleranced parts. It will also record the seed value used for each step. To open the log file, select menu Monte Carlo > View Log File or Simulator > Reports > Monte Carlo. The actual log data is stored in an XML data file and if there are multiple cores used, each core generates its own file. The above menus will compile an HTML report using those files as its input data and then display it. For a long run on a large circuit, this process may take a few seconds.