Using sprintf (problem with integer)

2017 4 27
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更新时间：2017 4 28
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Hi to everybody, I have got a problem using sprintf. I'm using it for doing the following operation:
step_value=sprintf('step%d',steps(i)*100);
..where "steps" is a simple array containing numbers with two decimals. The problem is that at i=9 I get:
steps(9)*100
ans = 55.0000
sprintf('%d',ans)
ans= 5.500000e+01
...which is not clearly in integer notation. I don't have problems for the other i-elements, just for i=9.
Someone knows what is it the problem? Thanks :)

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Andrea Bracchitta
Andrea Bracchitta 2017-4-27

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@Walter Roberson
I know this problem. Indeed, my variable steps=0.1:0.05:1.
However, before making the loop, I just write the following instruction:
steps=round(steps*100)/100;
In this way, all the "far" decimal numbers (due to floating point errors) should desappear and I should not have any problem. Am I saying something wrong in your opinion?

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Walter Roberson
Walter Roberson 2017-4-28
Imagine that you are using 2 digit decimal, starting from 5.33001 and you want to represent that as exact thirds.
5.33001 * 3 -> 15.99003
round(15.99003) -> 16
16/3 -> 5.3333333333333 ... infinitely in theory
5.3333333333333 to 2 decimal -> 5.33
and now you multiply that by 3
5.33 * 3 -> 15.99
Oops, you did not manage to find a value, X, such that X * 3 = 16 exactly.
This happens because 1/3 cannot be exactly represented in finite decimal.
The same difficulty happens in binary with respect to 1/10 : 1/10 cannot be represented exactly in finite binary. In binary it is .00011001100110011... When you take a finite leading portion of that and multiply it by 10, you get something that is not quite 1.

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