It looks like the 'spy' function ignores negative values (matplotlib
0.87.5).
In [30]:spy( ones( (5, 5) ) )[0].get_xdata()
Out[30]:
array([ 0.5, 0.5, 0.5, 0.5, 0.5, 1.5, 1.5, 1.5, 1.5, 1.5,
2.5, 2.5, 2.5, 2.5, 2.5, 3.5, 3.5, 3.5, 3.5, 3.5,
4.5, 4.5, 4.5, 4.5, 4.5])
In [31]:spy( -ones( (5, 5) ) )[0].get_xdata()
Out[31]:array([], type=Float)
regards,
r.