Why do I receive errors related to the "InputGroup" property when executing my existing code in the Control System Toolbox 6.0 (R14)?

My existing scripts developed with the Control System Toolbox 5.2.1 (R13SP1) execute without problem. However, when I run those same scripts in the Control System Toolbox 6.0 (R14), I receive errors similar to the following:

 Error in ==> stss_nastran_to_ss_hd at 447

   ss_model.InputGroup = [ ss_model.InputGroup; { i_gl', ...

       [inputs{group_index(i_gin),inp_group_index}, ' ', ...       inputs{group_index(i_gin),inp_label_index}] }];

 ??? Error using ==> lti.lticheck

 Invalid value for InputGroup property.

Answer 1

[MathWorks Support Team]

We have verified that the documentation associated with changes made to the "InputGroup" LTI property is missing in the Control System Toolbox User's Guide.

In the Control System Toolbox 5.2.1 (R13SP1) and earlier versions, the "InputGroup" LTI property is a cell array. This is documented in the Control System Toolbox User's Guide, accessed by typing the following at the MATLAB 6.5.1 (R13SP1) prompt:

web([docroot,'/toolbox/control/manipmod/ltisys17.html'])

However, the "InputGroup" has been changed to a structure beginning with the Control System Toolbox 6.0 (R14). This is documented in the Control System Toolbox User's Guide, accessed by typing the following at the MATLAB 7.0 (R14) prompt:

web([docroot,'/toolbox/control/manipmod/ltisys18.html'])

Please note that the CELL2STRUCT function is utilized to automatically resolve the incompatibility between these data types, i.e., structures and cell arrays. For more information about this function, please refer to the documentation accessed by typing "doc cell2struct" at the MATLAB prompt.

However, there are certain exceptional cases for which the CELL2STRUCT conversion will fail when executing your existing code with the Control System Toolbox 6.0 (R14) and later versions. For instance, it was valid that group names contained blanks (i.e., ' ') in the Control System Toolbox 5.2.1 (R13SP1); but in the Control System Toolbox 6.0 (R14) and later versions, this same code will fail to execute because a blank (i.e., ' ') is not a legal field name for a structure. Consequently, you will need to revise your existing code so as to build valid structures that are then assigned to, e.g., the "InputGroup" LTI property. For more information about creating valid structures, refer to the documentation accessed by typing the following at the MATLAB 7.0 (R14) prompt:

web([docroot,'/techdoc/learn_matlab/ch5pgm13.html'])