Re: [Matplotlib-users] showing an image on log axes?

[David H. <dav...@gm...>]

Hi,
Numpy has a logspace function, so it may be a bad idea to create a function
in pylab with the same name that does something slightly different.

def logspace(start,stop,num=3D50,endpoint=3DTrue,base=3D10.0):
    """Evenly spaced numbers on a logarithmic scale.

    Computes int(num) evenly spaced exponents from start to stop.
    If endpoint=3DTrue, then last exponent is stop.
    Returns base**exponents.
    """
    y =3D linspace(start,stop,num=3Dnum,endpoint=3Dendpoint)
    return _nx.power(base,y)


David



2006/6/15, Stefan van der Walt <st...@su...>:
>
> On Tue, Jun 13, 2006 at 06:21:22AM -0500, John Hunter wrote:
> > setting the xscale and yscale to 'log' should work fine, as long as
> > you make sure the xaxis and yaxis do not contain nonpositive limits.
> > For an MxN image, the default limits are 0..N-1 and 0..M-1 and the 0
> > will break the log transform.  You can work around this by setting the
> > image "extent"
> >
> >   from pylab import figure, show, nx
> >   fig =3D figure()
> >   ax =3D fig.add_subplot(111)
> >   im =3D nx.mlab.rand(500,500)
> >   ax.imshow(im, extent=3D(1,501,1,501))
>
> I often want to plot matrices, with the axes labeled according to the
> matrix index.  I.e. the top-lefthand element should be (0,0) and the
> bottom-righthand element (rows,columns).  Setting the extent does
> work, i.e.
>
> ax.imshow(im,extent=3D(1,columns,rows,1))
>
> If others also use this frequently, it may be useful to have a quick
> way of doing it (or maybe, there already is, and I've missed it).
>
> Regards
> St=E9fan
>
>
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