check value in matfile

I created a matfile as below..

tval=[1 2 3 4 5 6 7]
save filename tval;

now i have a variable whose value is 4...

now i want to check whether that value contains in the matfile... if it is there i want to display a message 'yes' and if not there display 'no'...

please can someone show me how to check whether the variable's values is in the matfile or not...

Answer 1

   S=load(filename,'tval');
   if ismember(4,S.tval),
    disp 'yes'
   else
    disp 'no',
   end

sir i'm getting error... its saying undefined function 'filename'

S=load('filename','tval');

thank u sir...