configure scale plotting

How to Get symmetric plotting in pylab....
i tried this code:
# -*- coding: utf-8 -*-

"""

Created on Sat Mar 10 20:33:32 2012

@author: fajar

"""

from numpy import linspace, meshgrid, array

import matplotlib.pyplot as pl

import matplotlib.ticker as tc

from scipy.integrate import odeint

# membuat vektor

u = linspace(-5,5,25)

v = linspace(-5,5,25)

U,V = meshgrid(u,v)

def fu(u,v): return 2*u-2*v

def fv(u,v): return 2*u-3*v

FU = fu(U,V)

FV = fv(U,V)

# sistem Persamaan:

def g(x,t):

y1 = 2*x[0]-1*x[1]

y2 = 1*x[0]-2*x[1]

return [y1, y2]

time = linspace(-1,-.6,100)

con = array([[1,2],[1.5,-3],[-1.5,3],[-1.5,-3]])

pl.figure()

Q = pl.quiver(U,V,FU,FV, units='height', hold=True)

#sol = odeint(g, con[0], time)

#pl.plot(sol[:,0], sol[:,1], linewidth=2.1 , color='y')

ยทยทยท

#

#sol = odeint(g, con[1], time)

#pl.plot(sol[:,0], sol[:,1], linewidth=2.1,color='b')

#

#sol = odeint(g, con[2], time)

#pl.plot(sol[:,0], sol[:,1], linewidth=2.1 , color='m')

#

#sol = odeint(g, con[3], time)

#pl.plot(sol[:,0], sol[:,1], linewidth=2.1 , color='r')

#

pl.autoscale(enable=True,axis='Both', tight=True)

#tc.AutoLocator()

tc.MaxNLocator(9,symmetric=True)

#pl.xlabel('u', weight='bold')

#pl.ylabel('v', weight='bold')

#pl.title('u\'=u dan v\'=-2v',weight='bold')

#pl.autoscale()z

pl.show()

---
but i get picture like in this attach... (aa.png)
what i need is to Make side of figure stright... not oblique...
like this attach (ab.png)...
with coresponding code:
# -*- coding: utf-8 -*-

"""

Created on Sat Mar 10 20:33:32 2012

@author: fajar

"""

from numpy import linspace, meshgrid, array

import pylab as pl

from scipy.integrate import odeint

# membuat vektor

u = linspace(-5,5,21)

v = linspace(-5,5,21)

U,V = meshgrid(u,v)

def fu(u,v):return u

def fv(u,v):return -2*v

FU = fu(U,V)

FV = fv(U,V)

# sistem Persamaan:

def g(x,t):

y1 = x[0]

y2 = -2*x[1]

return [y1, y2]

time = linspace(0,1,100)

con = array([[1.5,3],[1.5,-3],[-1.5,3],[-1.5,-3]])

pl.figure()

Q = pl.quiver(U,V,FU,FV, units='height', hold=True)

sol = odeint(g, con[0], time)

pl.plot(sol[:,0], sol[:,1], linewidth=2.1 , color='y')

sol = odeint(g, con[1], time)

pl.plot(sol[:,0], sol[:,1], linewidth=2.1,color='b')

sol = odeint(g, con[2], time)

pl.plot(sol[:,0], sol[:,1], linewidth=2.1 , color='m')

sol = odeint(g, con[3], time)

pl.plot(sol[:,0], sol[:,1], linewidth=2.1 , color='r')

pl.autoscale(enable=True,axis='Both', tight =True)

pl.xlabel('u', weight='bold')

pl.ylabel('v', weight='bold')

pl.title('u\'=u dan v\'=-2v',weight='bold')

pl.show()
--
i'm sorry, i didn't well to speak english, but i guess you know what mean... thanks before....

aa.png

ab.png