'Write variable at top level of mat file
Parameters
arr : array_like
array-like object to create writer for
name : str, optional
name as it will appear in matlab workspace
default is empty string
is_global : {False, True}, optional
whether variable will be global on load into matlab'

def write_top(self, arr, name, is_global):

    self._var_is_global = is_global
    self._var_name = name
    self.write(arr)
