Question

I m puzzled by some behaviour I m seeing when copying a float array member into another variable - please help!

例如

data_entry[1] = 9.6850069951

new_value = data_entry[1]


<comment> #print both

9.6850069951


9.6850663300

I m aware of the problem of binary storage of floats but I thought with a direct copy of memory we would end up with the same value.

Any ideas? I need better precision than this! thanks in advance Stuart

Answer 1

在转让后,变数的新价值不是浮标的复印件,它只是另外提到同一物体。因此,不可能有不同的印本。因此,在原始问题中无疑略去了一些细节。

斯图尔特——请你尝试以下工作并公布结果,或告诉我们你的实际法典如何变化。请注意,新的“数值是数据_enter? 即两者均为同一目标。

>> data_entry = [0,0]
>> data_entry[1] = 9.6850069951
>> new_value = data_entry[1]
>> new_value is data_entry[1]
True
>> print data_entry[1], new_value
9.6850069951 9.6850069951

Answer 2

如果您真正使用array模块(或numpy s ranges),那么精确损失很容易解释,例如:

>>> dataentry = array.array( f , [9.6850069951])
>>> dataentry[0]
9.6850070953369141

www.un.org/Depts/DGACM/index_french.htm 说我们再使用32个轨道浮标,因此只有大约7个重要数字“保险”。但是,很容易使用64轨浮动(在所谓的“双重精确”时):

>>> dataentry = array.array( d , [9.6850069951])
>>> dataentry[0]
9.6850069951000002

如你所看到,这样,十多位“保险”的重要数字(通常可以依靠约14+,除非你做算术的“oo”,如在人数上作非常接近的区别,这当然会损害你的准确性;-)

Answer 3

我的双线工作与关于含水层的2.6.2:

>>> data_entry = [1, 2]
>>> data_entry[1] = 9.6850069951
>>> new_value = data_entry[1]
>>> print data_entry[1]
--> print(data_entry[1])
9.6850069951
>>> print new_value
--> print(new_value)
9.6850069951

一种选择是转向使用 Dec物体:

>>> from decimal import Decimal
>>> data_entry[1] = Decimal( 9.6850069951 )
>>> new_value = data_entry[1]
>>> print data_entry[1]
--> print(data_entry[1])
9.6850069951
>>> print new_value
--> print(new_value)
9.6850069951

如果你重新失去精确性,这可能会有所帮助。

Answer 4

你们把一些法典排除在外。

>>> data_entry=[0,0]
>>> data_entry[1] = 9.6850069951
>>> 
>>> new_value = data_entry[1]
>>> print data_entry
[0, 9.6850069951000002]
>>> print new_value
9.6850069951
>>> print data_entry[1]
9.6850069951

该浮点号的<代码>repr和str正在产生不同的结果。我的猜测是,你颁布的法典没有提到这一区别。

Answer 5

此处为经过编辑的编码格式:

old code:
data = []
for data_entry in data:
    if (data_entry[1] != 0):
    value = data_entry[1]
    modlog(logging.INFO, raw value = %.12f ,data_entry[1])
    modlog(logging.INFO, value_in = %.12f , value)
output:
:INFO:raw value = 2.334650748292
:INFO:value_in  = 2.334685585881

new code:
data = array.array( d ) 
if (data[index] != 0):
    test_data = data[index]
    modlog(logging.INFO, raw data = %.12f , data[(index)])
    modlog(logging.INFO, test_data = %.12f , test_data)
output:
:INFO:raw data = 2.333840588874
:INFO:test_data= 2.333840588874

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