error decimal aproximation, extra decimal

why in Matlab 0.94-1=-0.0600000000000001? Why is there an extra decimal 1?

Answer 1

[James Tursa]

Welcome to the world of floating point arithmetic! See this link:

https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero

Bottom line ... 0.94 cannot be represented exactly in IEEE double precision. That trailing 1 is actually part of more digits in an exact floating point binary to decimal conversion:

>> fprintf('%.60f\n',0.94-1)
-0.060000000000000053290705182007513940334320068359375000000000

The 0.94 all by itself converted into decimal is:

>> fprintf('%.60f\n',0.94)
0.939999999999999946709294817992486059665679931640625000000000