On 4/29/11 12:31 AM, pratik wrote:
> On Friday 29 April 2011 12:56 PM, dileep kunjaai wrote:
>> Dear sir,
>> I am trying to make an array of varies from -60 to 90 with difference
>> 0.25. I tried the following command ...
>> >>import numpy as N
>> lat=N.array(xrange(-6000, 9000, 25), dtype=float)
>> print lat/100
xrange() (or range(), or np.arange()) is almost never the right solution
for floating point ranges, due to the intricacies of floating point
precision.
> lat =numpy.mgrid[-60:90:.25]
or np.linspace:
np.linspace(-60,90,((60.+90.)*4. + 1))
((60.+90.)*4. + 1) is the number of points you want -- the +1 because
you want both end points.
mgrid is usually used for 2-d (or higher) grids, though it looks like it
makes sense for this use, too, though note that it doesn't give you both
endpoints in this case. From the docs:
"""If the step length is not a
complex number, then the stop is not inclusive.
"""
and an example:
In [15]: np.mgrid[-1:3:.25]
Out[15]:
array([-1. , -0.75, -0.5 , -0.25, 0. , 0.25, 0.5 , 0.75, 1. ,
1.25, 1.5 , 1.75, 2. , 2.25, 2.5 , 2.75])
I think this is too bad, actually, because we're back to range()-type
tricks to get the end point:
In [20]: np.mgrid[-1:3.25:.25]
Out[20]:
array([-1. , -0.75, -0.5 , -0.25, 0. , 0.25, 0.5 , 0.75, 1. ,
1.25, 1.5 , 1.75, 2. , 2.25, 2.5 , 2.75, 3. ])
-Chris
--
Christopher Barker, Ph.D.
Oceanographer
Emergency Response Division
NOAA/NOS/OR&R (206) 526-6959 voice
7600 Sand Point Way NE (206) 526-6329 fax
Seattle, WA 98115 (206) 526-6317 main reception
chris.bar...@noaa.gov
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