kx = zeros(10,10)
for i in xrange(10):
    kx[i,:] = rand(10)-0.5

plot(0,kx,zrange=[-0.6,0.6])    

negative_mask = ones(len(kx[:,0]),len(kx[0,:]))
for j in xrange( len(kx[0,:]) ):
      for i in xrange( len(kx[:,0]) ):
            if ( kx[i,j].le(0)):
                negative_mask[i,j] = -1

kx = kx * negative_mask
plot(1,kx,zrange=[-0.6,0.6])