Imprecise Basic operations
2 visualizaciones (últimos 30 días)
Mostrar comentarios más antiguos
Hi everyone,
I am using Matlab 2009a. When I try to calculate
0.9 - 0.8 - 0.1
then the result is
-2.775557561562891 e-017
Close to zero, but not zero. Is it not possible to get a precise solution for a floating point operation? This minor imprecision has large implications for my programs.
Is there a way to get precise calculations? Why does matlab get this (quite easy task) wrong?
Thanks for your help!
1 comentario
James Tursa
el 13 de Jul. de 2011
You might find this FEX submission useful:
http://www.mathworks.com/matlabcentral/fileexchange/22239-num2strexact-exact-version-of-num2str
Respuesta aceptada
Nathan Greco
el 13 de Jul. de 2011
Welcome to the world of floating point computing.
A computer can't exactly represent most floating point numbers.
Example: Try calculating 3*(1/3) by hand, with writing out 1/3 to as many decimal places as you please. You will get .9999..., which is CLOSE to 1, but is not equal to 1 (which the true answer should be).
2 comentarios
Jan
el 13 de Jul. de 2011
+1: Exactly. The behaviour is neither "wrong" nor "inprecise". It simply demonstrates the limited precision.
Walter Roberson
el 13 de Jul. de 2011
Though if you go an infinite number of decimal places, 0.99999999999999.... (with infinite 9's) *is* equal to 1.
If you had an infinite number of bits, you could get an exact binary representation for 0.1 -- but of course no physically realizable computer can be infinite.
Más respuestas (1)
Ver también
Categorías
Más información sobre Introduction to Installation and Licensing en Help Center y File Exchange.
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!