Tk::Error: Can't use an undefined value as a HASH reference at Generate_traceabi
lity_matrix1.pl line 66.
 Tk callback for .button1
 Tk::__ANON__ at C:/Perl/lib/Tk.pm line 252
 Tk::Button::butUp at C:/Perl/lib/Tk/Button.pm line 111
 <ButtonRelease-1>
 (command bound to event)