Validate an IMAT_GROUP object.
out=validate(group)
[out,isvalid]=validate(group,'silent')
[out,isvalid,msg]=validate(group)
VALIDATE checks the input objects to make sure they are valid, and returns the output in an IMAT_GROUP. If none of the inputs are valid, OUT will be empty. Passing in the string 'silent' will suppress output.
OUT is an IMAT_GROUP containing the validated GROUP. ISVALID is an optional output specifying whether the input data was a valid IMAT_GROUP. If MSG is requested, it is a cell array of strings containing messages for what entities are not valid (empty if the object is valid). If not requested, VALIDATE will issue an error message.