蟒蛇数学,numpy模块不同的结果? [英] python math, numpy modules different results?
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问题描述
导入数学
math.cos(60.0 / 180.0 *)如何检查这个差异是否在机器精度内? math.pi)
- > 0.5000000000000001
进口numpy
numpy.cos(60.0 / 180.0 * numpy.pi)
- > 0.50000000000000011
解决方案
的差异似乎由格式化例程所引起只有:
>>> '%.30f'%math.cos(60./180.*math.pi)
'0.500000000000000111022302462516'
>>> '%.30f' %np.cos(60./180.*np.pi)
'0.500000000000000111022302462516'
注意 np.cos
返回 np.float64
而不是 float
,显然这个类型的默认打印方式是不同的。在常见的硬件上,它们都是以64位 double
的形式实现的,所以在精度上没有实际的差别。
I get slightly different results calculating the cosine of a value. How can I check that this difference is within machine precision?
import math
math.cos(60.0/180.0*math.pi)
-> 0.5000000000000001
import numpy
numpy.cos(60.0/180.0*numpy.pi)
-> 0.50000000000000011
解决方案
The difference seems to be caused by the formatting routines only:
>>> '%.30f' % math.cos(60./180.*math.pi)
'0.500000000000000111022302462516'
>>> '%.30f' % np.cos(60./180.*np.pi)
'0.500000000000000111022302462516'
Note that np.cos
returns np.float64
rather than float
, and apparently that type is printed differently by default. On common hardware, they're both implemented as 64-bit double
, so there's no actual difference in precision.
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