执行文件I / O时精度下降 [英] loss of precision in doing file I/O
问题描述
大家好，
我有一个疑问，我会尽可能清楚地向你揭露它，也许
它是不完全是主题，对不起。
我有几个双打矢量（一些计算的输出）和我
检查标准和点产品之间的产品
将它们存储在一个txt文件中，获得预期的结果。
向量是正交的，所以norm = 1和点产品给出了
类似于1.0e-18的东西，我认为它非常接近于零...
当我再次从txt文件中读取向量时，我检查相同的东西
我发现点积现在大约是1.0e-8。
这是正常的吗？有没有办法避免这种精度损失？
我在win2000上使用visual studio 6进行c ++编程。
感谢您的支持宝贵的帮助。
-
我的电子邮件地址中没有数字
"吉夫"写道：
我有一个疑问，我会尽可能清楚地向你展示它，也许它不完全是主题，对不起。
我有几个双打矢量（一些计算的输出），我检查
它们之间的标准和点积，然后将它们存储在txt文件中获得预期的结果。
向量是正交的，所以norm = 1，点积给出类似于1.0e-18的东西，我认为它非常接近于零......当我再次从txt文件中读取向量时，我检查了相同的东西
我发现点积现在大约为1.0e-8。
这是正常的吗？有没有办法避免这种精度损失？
我在win2000上使用visual studio 6进行c ++编程。
如果您阅读并使用>>写入文件和<<数据将被转换为字符表示，并将使用默认精度。
1.0e-8听起来像我期望的那样。您可以更改
精度[请参阅ios :: precision（）]或以二进制形式保存文件[请参阅
read（）和write（）]。
giff写道：大家好，
我有一个疑问，我会尝试将它暴露给你尽可能清楚，也许
它不完全是主题，对不起。
我有几个双打矢量（一些计算的输出）和我
在将它们存储在txt文件中之前检查它们之间的规范和点积，得到预期的结果。
向量是正交的，因此norm = 1，点积给出
像1.0e-18这样的东西我认为非常接近于零...
当我再次从txt文件中读取向量时，我会检查相同的东西
和我发现点积现在大约是1.0e-8。
这是正常的吗？有没有办法避免这种精度损失？
请参阅此常见问题及以下内容：
http://www.parashift.com/c++-faq-lit...html#faq-29.16
你能告诉我们一个*完整*但*最小*的代码片段，我们可以削减
并粘贴到我们的编辑器中试试吗？这可能是用户错误。
我在win2000上使用visual studio 6在c ++中编程。
不相关。 （如果它是相关的，你就在错误的新闻组中。）
干杯！ --M
giff写道：我有几个双打矢量（一些计算的输出）和我在将它们存储在txt文件中之前检查它们之间的规范和点积，得到预期的结果。
向量是正交的，因此norm = 1和点产品给出了类似于1.0e-18的东西，我认为它非常接近于零...
当我再次从txt文件中读取向量时，我检查相同的
事情我发现点积现在大约是1.0e-8。
这是正常的吗？有没有办法避免这种精度损失？
在输出中写下更多数字。
我在win2000上使用visual studio 6在c ++中编程。
这没关系。
V
-
请删除资金''A'通过电子邮件回复
我没有回复最热门的回复，请不要问
Hi all,
I have a doubt, I''ll try to expose it to you as clearly as I can, maybe
it is not completely in topic, sorry about that.
I have a few vectors of doubles (output of some calculations) and I
check the norm and the dot product between couples of them before
storing them in a txt file, obtaining the expected results.
The vectors are orthonormal so the norm=1 and the dot product gives
something like 1.0e-18 that I suppose is quite close to zero...
When I read the vectors again from the txt file, I check the same things
and I find that the dot product is now around 1.0e-8.
Is this normal? Is there a way to avoid this loss of precision?
I am programming in c++ using visual studio 6 on win2000.
Thanks for your precious help.
--
there are no numbers in my email address
"giff" writes:
I have a doubt, I''ll try to expose it to you as clearly as I can, maybe it
is not completely in topic, sorry about that.
I have a few vectors of doubles (output of some calculations) and I check
the norm and the dot product between couples of them before storing them
in a txt file, obtaining the expected results.
The vectors are orthonormal so the norm=1 and the dot product gives
something like 1.0e-18 that I suppose is quite close to zero...
When I read the vectors again from the txt file, I check the same things
and I find that the dot product is now around 1.0e-8.
Is this normal? Is there a way to avoid this loss of precision?
I am programming in c++ using visual studio 6 on win2000.
If you read and write to the file using >> and << the data will be converted
to a character representation and the default precision will be used.
1.0e-8 sounds about like what I would expect. You could change the
precision [see ios::precision() ] or save the file in the binary form [see
read() and write()].
giff wrote:Hi all,
I have a doubt, I''ll try to expose it to you as clearly as I can, maybe
it is not completely in topic, sorry about that.
I have a few vectors of doubles (output of some calculations) and I
check the norm and the dot product between couples of them before
storing them in a txt file, obtaining the expected results.
The vectors are orthonormal so the norm=1 and the dot product gives
something like 1.0e-18 that I suppose is quite close to zero...
When I read the vectors again from the txt file, I check the same things
and I find that the dot product is now around 1.0e-8.
Is this normal? Is there a way to avoid this loss of precision?
See this FAQ and those following:
http://www.parashift.com/c++-faq-lit...html#faq-29.16
Can you show us a *complete* but *minimal* code snippet that we can cut
and paste into our editors to try it? It may be user error.
I am programming in c++ using visual studio 6 on win2000.
Irrelevant. (If it is relevant, you''re in the wrong newsgroup.)
Cheers! --M
giff wrote:I have a few vectors of doubles (output of some calculations) and I
check the norm and the dot product between couples of them before
storing them in a txt file, obtaining the expected results.
The vectors are orthonormal so the norm=1 and the dot product gives
something like 1.0e-18 that I suppose is quite close to zero...
When I read the vectors again from the txt file, I check the same
things and I find that the dot product is now around 1.0e-8.
Is this normal? Is there a way to avoid this loss of precision?
Write more digits to the output.
I am programming in c++ using visual studio 6 on win2000.
That shoulnd''t matter.
V
--
Please remove capital ''A''s when replying by e-mail
I do not respond to top-posted replies, please don''t ask
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