After normalizing vectors, slope field graph does not look normalized. Help.

I am trying to normalize the slope field to get a nice looking graph. However, I am not sure what I am doing wrong because I thought that I normalized the vectors. I must have a small mistake somewhere, but I am not sure where. I have attached a mat file with the values that I am using.

Here is the code:

function slope(aR,bR,aF,bF,y0,a_x,b_x,a_y,b_y,h_x,h_y,M)

r=a_x:h_x:b_x;

f=a_y:h_y:b_y;

[R,F] = meshgrid(r,f);

dr = aR.*R.*(1-(R./M))-bR.*R.*F;

df = aF.*R.*F-bF.*F;

d = sqrt( dr.^2 + df.^2 );

pr = dr./(d+0.0001);

pf = df./(d+0.0001);

quiver(R,F,pr,pf,0.5,'Color','k','ShowArrowHead','off');

axis tight;

axis([a_x b_x a_y b_y])

Here is the image of the slope field:

Thank you so much for your help in advance.