Frequently asked questions

This page provides answers to frequently asked questions about developing PACZ component plug-ins.

Variables and data types

Q1: How do I programmatically define a ModelCenter assembly in the component tree?

A1: Write nested variable names using "." separators:

• ModelCenter takes care of assembly creation automatically:
  
• Then use the same name in the RunAsync method to access the nested variable:
  

Q2: What characters are allowed for plugin variable names?

A2: PACZ variables use the same convention as Java variables, except dollar signs are not supported.

• Essentially alphanumeric + underscore, but the first character must be either a letter or underscore
• Periods are only supported as the separator between different levels of a hierarchy
• Spaces, punctuation, and special characters are not allowed

Q3: How do I access value and default value from the runner context?

A3: Access both read-only values as follows:

• Accessing DefaultValue is done with integer index rather than name. The user must search (using LINQ or a traditional iterator) through the available indices to find the desired name/DefaultValue. You are technically reading directly from the PACZ file created during the Builder context
• Note that Value can only be accessed from the Runner context. There is no access to Value from the Builder context
• In the Builder context, only DefaultValue can be set, which is later copied to create the variable's Value. This copy process is the responsibility of the host process, such as ModelCenter.

Q4: How do I create an array variable?

A4: Using a two-item Boolean array as an example:

bool[] val = { true, false };  
BooleanArrayValue booleanArrayValue = val;  
RuntimeVariable boolVar = new RuntimeVariable("bool_arr_var", VariableType.BooleanArray, booleanArrayValue);  

File and path handling

Q5: Is it possible to query relative path from inside the plugin?

A5: The plugin's model object is aware of both relative and absolute paths:

Note that the FilePath property changes depending on whether the path is inside or outside the extraction folder:

Variable management

Q6: How do I remove a single input/output variable from the model?

A6: Create a function like the following: _removeOutput(viewModel, "x2");

private void _removeOutput(VariableBasedBuilderViewModel viewModel, string outputToRemove)  
{  
    IEnumerable<IRuntimeVariable> oldOutputs = viewModel.OutputVariables;
    List<IRuntimeVariable> listToPopulate = new List<IRuntimeVariable>() { };
    foreach (var item in oldOutputs)
    {
        if (item.Name != outputToRemove)
        {
            listToPopulate.Add(item);
        }
    }
    IEnumerable<IRuntimeVariable> newOutputs = listToPopulate;
    viewModel.MoveOutputVariablesFrom(newOutputs);
}

Q7: How do I define a file as an output variable?

A7: During output list construction you would have:

private IEnumerable<IRuntimeVariable> _createOutputs()
{
    RuntimeVariable y = new RuntimeVariable("y", VariableType.Real, new RealValue(0.01));
    RuntimeVariable outvar = new RuntimeVariable("NASTRANMAP", VariableType.File, FileValue.CreateFromString(null, null, "c:\\thermal\\stress\\case1.txt", null));

    IEnumerable<IRuntimeVariable> outputs = new List<IRuntimeVariable>() { y, outvar };
    return outputs;
}

During execution time:

public async Task RunAsync(IReadOnlyDictionary<string, VariableState> inputs, VariableValueScope outputs, CancellationToken cancellation)
{
    //TODO: Run the component, set the outputs as a function of the inputs
    // e.g.
    double x1 = (RealValue)inputs["a1.a2.x1"].SafeValue;
    double x2 = (RealValue)inputs["x2"].SafeValue;
    outputs["y"] = new VariableState(new RealValue(x1*x2));

    FileValue outvarOld = (FileValue) outputs["NASTRANMAP"].SafeValue; 
    outputs["NASTRANMAP"] = new VariableState(FileValue.ReadFromFile(outvarOld.OriginalFileName));

    await Task.CompletedTask;
}

Q8: How do I determine the type of an input variable at runtime?

Question: From the runner context, I can iterate through input variables using foreach (var key in inputs.Keys). I need to determine whether each input is type string or type real. I currently have (StringValue)inputs[key].SafeValue. That crashes when it is a real. Is there a way to check what type of input it is?

A8: There are several ways, depending on your use case.

The simplest is to just use SafeValue.VaraibleType, which is an enumeration of all the possible types (Integer, Real, String, Boolean, File, IntegerArray, RealArray, StringArray, BooleanArray, FileArray).

You can also use the safe type conversion capabilities of C# such as inputs[key].SafeValue As StrinValue, which returns the converted value or null if it is not the correct type.

Q9: How do I create a multi-dimensional array?

A9: Example using integers:

long[,] intArr = new long[3, 4] {
   {0, 1, 2, 3} ,   /*  initializers for row indexed by 0 */
   {4, 5, 6, 7} ,   /*  initializers for row indexed by 1 */
   {8, 9, 10, 11}   /*  initializers for row indexed by 2 */
};
IntegerArrayValue intArrVal = new IntegerArrayValue(intArr);
RuntimeVariable x3 = new RuntimeVariable("x3", VariableType.IntegerArray, intArrVal);

Q10: How do I add a description to an IRuntimeVariable instance?

A10: See the x3 variable definition in the BasicPaczPlugin example.