How to round the decimals?

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Isti
Isti 2012-5-3
评论： Walter Roberson 2021-5-18
I have a number X = 0.135678
Then i just want to round it become 0.14. What to do?
Use round(X) will only give "0".
Thanks before :)
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Walter Roberson
Walter Roberson 2021-5-18
@Mahaveer Singh
Right, these days round() in MATLAB supports passing in the number of decimal digits. When the question was originally asked, that option was not available.
Also, some of the users were needing to work in Simulink, but the round block https://www.mathworks.com/help/simulink/slref/roundingfunction.html does not support giving a number of decimal digits.

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采纳的回答

Jos (10584)
Jos (10584) 2014-2-11
编辑：Stephen23 2015-11-11
A = [pi exp(1) 1/7]
Ndecimals = 2
f = 10.^Ndecimals
A = round(f*A)/f

更多回答（7 个）

Walter Roberson
Walter Roberson 2012-5-3
Computationally it cannot be done: binary floating point arithmetic is not able to exactly represent most multiples of 0.01.
http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F
Steven Lord
Steven Lord 2016-11-7
As of release R2014b you can use the round function in MATLAB to round to a specific number of decimal places.
Vladimir Melnikov
Vladimir Melnikov 2020-4-29
编辑：Vladimir Melnikov 2020-4-29
the easiest way:
round (X,N)
e.g:
>> round(0.12345,1)
ans = 0.100000000000000
>> round(0.12345,2)
ans = 0.120000000000000
>> round(0.12345,3)
ans = 0.123000000000000
also read
>> doc round
Andrei Bobrov
Andrei Bobrov 2012-5-3
use roundn from Mapping Toolbox
roundn(X,-2)
  1 个评论
Vladimir Melnikov
Vladimir Melnikov 2020-4-29
roundn(1.12345,-1)
ans = 1.100000000000000
>> roundn(1.12345,-2)
ans = 1.120000000000000
>> roundn(1.12345,-3)
ans = 1.123000000000000

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Wayne King
Wayne King 2012-5-3
One way here is:
X = 0.135678;
format bank;
X
Another way is:
format; %just returning the formatting
X = ceil(X*100)/100;
Probably the last way is the best because you don't have to mess with the formatting.
Prateek Sahay
Prateek Sahay 2016-11-7
If you want to round 1.556876 to three decimal places then multiply it with 1000 and the use round command and then again divide it by 1000. X=1.556876 X=X*1000 Means now X=1556.876 round(x) Means now X=1556.9 X=X/1000 Means now X=1.5569
  1 个评论
Walter Roberson
Walter Roberson 2016-11-7
That is what Jos's Answer does; http://www.mathworks.com/matlabcentral/answers/37262-how-to-round-the-decimals#answer_124002.
Note that the result of the round() would be 1557 not 1556.9
Note that the result will not be exact. There is no way to represent exactly 1.557 in binary floating point. The closest it gets is 1.556999999999999939603867460391484200954437255859375
This will display as 1.557 in most output modes, but it will not be exactly that value.

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Jason Garcia
Jason Garcia 2019-2-7
编辑：Jason Garcia 2019-2-7
Maybe not exactly what you're looking for, but if you are looking for ceiling or floor measurements the below is a fun way to specifiy directly how you want to bin the array/value.
X = rand(100,1); %Rand 100 elmnt vector w/ range 0-1.
n = 100; %Use 100 for the nearest tenth.
cX = discretize(X,[0:1/n:1],[0+1/n:1/n:1]); %Rounds X UP to nearest 1/N.
%OR
fX = discretize(X,[0:1/n:1],[0:1/n:1-1/n]); %Rounds X DOWN to nearest 1/N.

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