code: public SystemInputDef addFunctionInputDef( FunctionInputDef functionInputDef)
      {
      assert functionInputDef != null;
      assert functionInputDef.getName() != null;
  
      if( findFunctionInputDef( functionInputDef.getName()) >= 0)
        {
        throw new IllegalStateException( "Function=" + functionInputDef.getName() + " already defined for system=" + getName());
        }
      
      functionInputDefs_.add( functionInputDef);
      return this;
      }
docs: Adds a new function definition.