How to comparison decimal numbers

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Thar
Thar 2015-12-1
评论： Walter Roberson 2015-12-2
Hi all!
I have two matrices. They have one column. First matrix is:
7.551119
7.551154
7.551189
7.551224
Second matrix is:
7.551111
7.551146
7.551181
7.551215
I want to comparison two columns but only 5 decimal places. I don't like round my numbers like:
7.55112
7.55115
and so on, if I use the function round.
  2 个评论
Walter Roberson
Walter Roberson 2015-12-1
When you say that you want to compare to 5 decimal places, do you mean that when printed out rounded to 5 decimal places the numbers must match, or do you mean that the difference between the two numbers must be less than 10^(-5) ? Or at most 1/2 * 10^(-5) ?
Thar
Thar 2015-12-2
I want to keep the 5 decimal points, but not rounded the numbers. for example for the number 7.551187 i want to keep only the 7.55118 and not round to 7.55119.

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采纳的回答

arich82
arich82 2015-12-2
You can truncate (without rounding) using floor (or fix, if your numbers can be negative):
x = [ ...
7.551119; ...
7.551154; ...
7.551189; ...
7.551224; ...
];
y = fix(x*1e5)/1e5;
output:
y =
7.551110000000000
7.551150000000000
7.551180000000000
7.551220000000000

更多回答（2 个）

Image Analyst
Image Analyst 2015-12-2
You need to use a tolerance. See the FAQ for a complete explanation: http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F
Thorsten
Thorsten 2015-12-2
编辑：Thorsten 2015-12-2
You can round to 5 decimal places using
xr = round(x*1e5)/1e5;
You may want to set
format long
such that the result is properly displayed.
  5 个评论
显示 3更早的评论
Image Analyst
Image Analyst 2015-12-2
Then don't round (as I suspected you shouldn't). Use the tolerance like I told you in my answer where I referred you to the FAQ.
Walter Roberson
Walter Roberson 2015-12-2
To check, Thodoris, you are okay with 7.551111 comparing equal to 7.551119, but 7.551119 should not compare equal to 7.551121 even though that is closer to it than 7.551111 is?

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