public DifferentialFunction getFunctionById(String id) {
        if (!functionInstancesById.containsKey(id)) {
            throw new ND4JIllegalStateException("No function with id " + id + " found!");
        }
        return functionInstancesById.get(id);
    }
public DifferentialFunction getFunctionById(String id) {
        if (!functionInstancesById.containsKey(id)) {
            throw new ND4JIllegalStateException("No function with id " + id + " found!");
        }
        return functionInstancesById.get(id);
    }
public DifferentialFunction getFunctionById ( String id ) { if ( ! functionInstancesById . containsKey ( id ) ) { throw new ND4JIllegalStateException ( "No function with id " + id + " found!" ) ; } return functionInstancesById . get ( id ) ; }
Get the function by the {@link DifferentialFunction#getOwnName()}

@param id the id of the function
@return the function for the given id if it exists
Get the function by the { @link DifferentialFunction#getOwnName () }