%----- snip 

function richtungsfeld(dgl)

y = -5:.5:5; 

x = -5:.5:5;

for y_n = 1:length(y)

 for x_n = 1:length(x)

   len = sqrt( dgl(y(y_n), x(x_n))^2 + 1 ); 

   dx(y_n,x_n) = 1 / len;                   

   dy(y_n,x_n) = dgl(y(y_n), x(x_n)) / len; 

 end

end 

h=quiver(x, y, dx, dy,0.5,"r","linewidth",1); 

set (h, "maxheadsize", 0.1); 

xlabel ("x");

ylabel("y");

print('field.svg', '-dsvg')  

%-----snap

then run three octave commands

 source("richtungsfeld.m")
 dgl = @(y, x) y-x  
 richtungsfeld(dgl)