How to comparison decimal numbers

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Thar 2015-12-1

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评论： Walter Roberson 2015-12-2

采纳的回答： arich82

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Hi all!

I have two matrices. They have one column. First matrix is:

Second matrix is:

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.

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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 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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Answer 1

arich82 2015-12-2

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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 =
551110000000000
551150000000000
551180000000000
551220000000000

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Thar 2015-12-2

Thank you!!

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Answer 2

Image Analyst 2015-12-2

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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

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Answer 3

Thorsten 2015-12-2

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编辑：Thorsten 2015-12-2

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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.

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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 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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