Same line length in slope fields

[scidam]

You need to define line length first.

from pylab import plt, np
def f(x,y):
    return -y/x

line_len = 0.2

for m in [i for i in range(-4,5) if i!=0]:
    for n in [i for i in range(-4,5) if i!=0]:
        slope=f(m/2,n/2)
        slope = np.arctan(slope)   # we need to clarify what slope means, is it an angle? or tan(angle)? what do we want?
        plt.plot([m/2,m/2+line_len * np.cos(slope)],[n/2,line_len * np.sin(slope)+n/2],color='k')
        plt.ylim(-2,2,1/2)
        plt.xlim(-2,2,1/2)
        plt.grid(True)