How to increase filter length until required number of solutions is reached

I need to run a filter while increasing its length until the required number of solutions is reached. How should I define the variable 'index' to make the following 'while loop' function.

while length(index)>8
    n = 20;
    filtered_ipam_relative_hand_position = moving_average_filter(ipam_relative_hand_position, n);
    velocity=zeros(size(filtered_ipam_relative_hand_position));
    for i = 1:length(data)
    for j = 1:3
        x = i-1;
        y = i+1;
        if x == 0
            x = 1;
        else
            if i == length(data)
                y = length(data);
            end
        end
        velocity(i,j) = (filtered_ipam_relative_hand_position(y,j)- filtered_ipam_relative_hand_position(x,j))/0.08;
    end
    end
     magnitude_velocity = zeros(length(velocity),1);
     for i=1:length(data)
         magnitude_velocity(i)=((velocity(i,1))^2 + (velocity(i,2))^2 + (velocity(i,3))^2)^0.5;
     end
     for i=1:length(data)-1
         if (magnitude_velocity(i+1,1)<0.01) && (magnitude_velocity(i,1)>0.01)
           index = [index i];
         end  
     end
     n = n+1;
end

[Walter Roberson]

How does this differ from your previous question http://www.mathworks.co.uk/matlabcentral/answers/68166-increasing-value-of-filter-till-required-number-of-solutions-each-reached ?

[Afzal]

Its the same question but I don't know how to define the variable 'index'.