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Numerical errors of basic multiple

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yifwang
yifwang 2019-8-26
评论： yifwang 2019-8-26
When using matlab multiple calculation, some errors happen
a = 7*13e-6;
b = 6*13e-6;
the answer is
a = 9.09999999999999999e-5
b = 7.80000000000000000e-5
erroe happened at a but not at b;
So how this error happen and how * works? On what condition the error happen?
  2 个评论
KALYAN ACHARJYA
KALYAN ACHARJYA 2019-8-26
Error?
>> a =13e-6
a =
1.300000000000000e-05
>> 7*a
ans =
9.099999999999999e-05
yifwang
yifwang 2019-8-26
7*13e-6 should be exactly
9.100000000000000e-5
but not
9.099999999999999e-5
error

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采纳的回答

Ted Shultz
Ted Shultz 2019-8-26
These are floating point calculations. Not every number can be represented, and this rounding error can compound when you do math with these imperfect numbers.
"Floating-point error arises because real numbers cannot, in general, be accurately represented in a fixed space."
https://en.wikipedia.org/wiki/Floating_point_error_mitigation

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