how to get percentage of SVM result?

Hello every one i'm glad if some one can help or answer me, my problem is I want to get SVM percentage of SVM after classifying test with train, I've 56 img for train and 2 img for test I tried by these code but always give me 0.5000 which is mean 50 % percentage even I changed test imgs is the same result.

test_row =2;
  for s=1:56
  for j=1:test_row

        [c1(s)] = svmclassify(struct,test_img(j,:));

    end
    end

    for t=1:length(c1)
        if c1(t)==2;
           c1(t)=0;
        end
    end
    F=sum(c1(1:28))/28;    
    M=1-sum(c1(29:56))/28; 
    average=(F+M)/2

thank you.........