why there is a small error in these simple calculations?

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Zixuan Li 2019-4-11

编辑： Stephen23 2019-4-11

3e-4-3*10^-4
 sum=0;
			for i=1:1000
			   sum=sum+0.001;
			end
			sum_output=sum

this gives an answer of -5.421010862427522e-20 and 1.000000000000001

it should be obviously 0 and 1. what happened during the running of program??

Stephen23 2019-4-11

编辑：Stephen23 2019-4-11

"it should be obviously 0 and 1. "

Nope. Not with binary floating point numbers.

Search this forum for "floating point" and you will learn the reasons why this happens.

Star Strider 2019-4-11

See the documentation on Floating-Point Numbers (link).

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