Why do I get zero?

2 次查看（过去 30 天）
StewJo
StewJo 2011-6-24
Running 7.10.0 (R2010a) under Windows 7 on an Intel i5 (Lenovo laptop):
K>> TAhi
TAhi = -8.6578e+009
K>> TAlo
TAlo = -8.6578e+009
K>> TAhi/2.0 - TAlo/2.0
ans = 9.5367e-007
K>> (TAhi+TAlo)/2.0 - TAlo
ans = 0
Why do I get 0 when I should get 9.5367e-007 ? I wouldn't image e-007 is anywhere near machine tolerance.
Any help is appreciated!

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采纳的回答

Nirmal Gunaseelan
Nirmal Gunaseelan 2011-6-24
The next highest floating point number representable relative to the current number is probably the issue here. Please read further at EPS documentation page.

更多回答（2 个）

Fangjun Jiang
Fangjun Jiang 2011-6-24
Maybe you can type in the following command and then do your calculation again to see the difference
format long
David Young
David Young 2011-6-24
(TAhi-TAlo)/TAhi is close to machine precision, and it's this relative size that matters when comparing two almost equal numbers.

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