[Gnuplot-py-users] Gnuplot.py float precision (again)

[Xaver W. <xav...@we...>]

Hi guys,

I'm sorry to bring this up again, but I'm about to publish my code and I'd 
really love to get this straight/fixed. In case you don't remember, I'm 
trying to plot high precision numbers (float64, that is), but gnuplot.py 
converts them to float32 arrays. 
Michael Haggerty told me to 'workaround' by using numpy double arrays, but it 
seems that's not working here. I think the problem might be here: 
(/usr/share/pyshared/Gnuplot/utils.py, line 20ff)

>def float_array(m):
>    """Return the argument as a numpy array of type at least 'Float32'.
>
>    Leave 'Float64' unchanged, but upcast all other types to
>    'Float32'.  Allow also for the possibility that the argument is a
>    python native type that can be converted to a numpy array using
>    'numpy.asarray()', but in that case don't worry about
>    downcasting to single-precision float.
>
>    """
>
>    try:
>        # Try Float32 (this will refuse to downcast)
>        return numpy.asarray(m, numpy.float32)
>    except TypeError:
>        # That failure might have been because the input array was
>        # of a wider data type than float32; try to convert to the
>        # largest floating-point type available:
>        # NOTE TBD: I'm not sure float_ is the best data-type for this...
>        try:
>            return numpy.asarray(m, numpy.float_)
>        except TypeError:
>            # TBD: Need better handling of this error!
>            print "Fatal: array dimensions not equal!"
>            return None

If I understand this correctly, the line
> return numpy.asarray(m, numpy.float32)
is supposed to raise a TypeError if you give a numpy.float64 array.
However, my python shell doesn't:

>(00:13:52)xaver@siduxbox:~$python
>Python 2.5.4 (r254:67916, Feb 18 2009, 03:00:47)
>[GCC 4.3.3] on linux2
>Type "help", "copyright", "credits" or "license" for more information.
>>>> import numpy
>>>> a = numpy.array( [2.000000001,3.0,4.0] )
>>>> a.dtype
>dtype('float64')
>>>> numpy.asarray(a, numpy.float32)
>array([ 2.,  3.,  4.], dtype=float32)

Am I doing sth wrong? Can anyone confirm that?

Thanks in advance,
Xaver