question concerning rounding of numbers

Hi

I am having trouble rounding a number to a fixed number of digits. Can anyone explain the problem I am encountering? (As shown in this figure)

Answer 1

[James Tursa]

See also this link:

http://www.mathworks.com/matlabcentral/answers/185019-matlab-round-function-not-rounding-small-decimals-away

[John D'Errico]

As has been said, no matter how hard you try, you cannot represent 30.7 exactly as a double precision number. That is a binary representation, and your number is not exactly representable.

In fact, this is true of almost all the numbers you will write in decimal form. The exceptions are integers of a reasonable size, and those numbers that can be written as sums of limited negative powers of 2. So 0.5, and 0.375 will be exactly represented.

Answer 2

[Luuk van Oosten]

Yes, I believe your problem is described here

Answer 3

[Jakob Sievers]

Thanks for all of your comments. They helped me greatly!