Matlab - Avance de posicion de un bucle

for i=1:1:2

    for j=i+1:1:5

        if nod_dif_vig(i,3)==nod_dif_vig(j,3)

            nod_fin_vig(pos_fin_vig,1)=nod_dif_vig(j,1);

            pos_fin_vig=pos_fin_vig+1;

            i=i+1

        else

        end

    end

end

clear all

    i=1;

    while i<=2

        for j=i+1:1:5

          if round(rand(1))==round(rand(2))

            'cumple'

            %if nod_dif_vig(i,3)==nod_dif_vig(j,3)

            %nod_fin_vig(pos_fin_vig,1)=nod_dif_vig(j,1);

            %   pos_fin_vig=pos_fin_vig+1;

            i=i+1;

          end

        end

    end