EXTREMELY WEIRD arithmetic bug

Question

louise 2011-8-3

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/12996-extremely-weird-arithmetic-bug

Hi there,

Basically I'm adding 0.001 to a number over and over again. The series starts with zero so the resulting number should ALWAYS be a multiple of 0.01, but instead it eventually degenerates into numbers like 5.874000000000296 - obviously NOT a multiple of 0.001!

Can you explain why? Can it REALLY BE that Matlab just can't cope with numbers of that precision? It's a mathematics package!!!

Run the following code to reproduce the bug. I'm running 7.10.0(R2010a).

Just run log=testcase() and then inspect the latter half of log in the variable editor- when you double-click on a cell to expand it you will be able to see the lack of precision.

function [ log ] = testcase( )
%RUN LIKE THIS: log=testcase()
%Then inspect the log in the variable editor.
    runTime=20;
    t=0;
dx=0.001;
i=1;
log(i,1)=t;
it=2;
for i=2:runTime/dx
      t=t+dx;
log(i,1)=t;
end
end