private void computeBias(double ai, double aj, int yi, int yj, double kii, double kjj, double kij) {
                double b1 = model.b - Ei - yi*(ai-ai_old)*kii - yj*(aj-aj_old)*kij;
                double b2 = model.b - Ej - yi*(ai-ai_old)*kij - yj*(aj-aj_old)*kjj;
                if (0 < ai && ai<C)
                        model.b = b1;
                else if (0 < aj && aj < C)
                        model.b = b2;
                else
                        model.b = (b1+b2)/2;            
        }