# Numerical errors of basic multiple

15 views (last 30 days)
yifwang on 26 Aug 2019
Commented: yifwang on 26 Aug 2019
When using matlab multiple calculation, some errors happen
a = 7*13e-6;
b = 6*13e-6;
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?
KALYAN ACHARJYA on 26 Aug 2019
Error?
>> a =13e-6
a =
1.300000000000000e-05
>> 7*a
ans =
9.099999999999999e-05
yifwang on 26 Aug 2019
7*13e-6 should be exactly
9.100000000000000e-5
but not
9.099999999999999e-5
error

Ted Shultz on 26 Aug 2019
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."
Ted Shultz on 26 Aug 2019

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