# how to find out if a number is even or not

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divya r 2012 年 10 月 23 日
コメント済み: Walter Roberson 2021 年 10 月 28 日
I know in C language, for any number x using x%2 will calculate the remainder when x is divided by 2, which will help decipher whether its even or not.
How can I do this in matlab?
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Steven Lord 2020 年 10 月 9 日
So Inf is even?
>> s = (-1)^Inf
s =
1
>> s = (-1)^NaN
s =
NaN
Does this hold for a complex number as well?
>> N = 3+4i;
>> s = (-1)^N; % Not equal to -1

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### 採用された回答

Walter Roberson 2012 年 10 月 23 日

See mod and rem
##### 1 件のコメント表示非表示 なし
Dillen.A 2020 年 2 月 5 日
A quick example:
A = [-2 -1 0 1 2 3 4 5 6]; % A is your value or matrix
IS_EVEN = ~mod(A,2)
Which is the same as
IS_EVEN = ~bitget(abs(A),1)
And the same as
IS_EVEN = ~rem(A,2)
You can use logical() instead of ~ (isnot) for ODD, should you want booleans. Also bitget() does not work for negative integers, hence abs().
A warning though; ONLY bitget() will throw an error if an element in A is not an integer! the others will output 'odd' for fractions.
Unless you will repeat this many many times, the speed is not relevant. Otherwise, you should vectorize.

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### その他の回答 (8 件)

Jan 2012 年 10 月 23 日
Care for exceptions:
NaN, Inf, 1e54, int8(-128)
There are some FEX submission for this task, e.g. FEX: parity checker.
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Matt J 2012 年 10 月 23 日
if bitget(A,1) %odd
else %even
end
##### 2 件のコメント表示非表示 1 件の古いコメント
Josh Meyer 2018 年 10 月 10 日
In more recent versions of MATLAB, bitmax was replaced by flintmax. This is the largest consecutive floating point number. After flintmax, the value of eps is larger than 1 (slowly increasing in powers of 2), so representable numbers larger than flintmax are no longer consecutive.
So, the reason all of those numbers are even is because flintmax is an even number and the spacing between numbers is eps(flintmax) = 2.

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luis fonseca 2020 年 10 月 9 日
This is the easiert way guys, its just math from highschool
N = 1; % number you want to know if even or odd
%% create an expression
s = (-1)^N;
%% if s = -1, the N is odd, else N is even
if s == -1
disp('N is odd')
else
disp('N is even')
end
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Howard Lam 2021 年 10 月 15 日
use .^

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Ibn e Adam 2020 年 2 月 18 日
% function to find even/odd
% n is input number for this function
function output=even_or_odd(n)
if rem(n,2)==0
output=even;
else
output=odd;
end
end
##### 4 件のコメント表示非表示 3 件の古いコメント
Matt J 2020 年 2 月 26 日
not in inverted commas
I guess inverted commas = single quotes

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Anmol singh 2020 年 4 月 10 日

A givennumber is even or odd for this we use & operator.
if any number is odd it must have right most bit 1.
example:
int i=5;
binary form i= 0101
now use & operator
int j=i&1;[0101&1]//
here j have 0001;
##### 1 件のコメント表示非表示 なし
Walter Roberson 2020 年 4 月 10 日
This does not work in MATLAB. In MATLAB, the operation
c = A & B
is equivalent to
if A ~= 0
if B ~= 0
c = true;
else
c = false;
end
elseif B ~= 0
c = false;
else
c = false;
end
Yes, this could be made more efficient, but this models the & operator. The more efficient operation is &&
Now notice that this is not a bitwise operation. 5&1 is not binary 0101 & 0001 giving 0001: instead it is (5~=0) and (1 ~= 0)
The MATLAB equivalent to what you are discussing is the bitand() operator
bitand(5,1)
But if you are going to do that, you might as well just ask for the last bit directly:
bitget(5,1) %the 1 is a bit number with LSB being #1

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Matt J 2020 年 10 月 9 日

One more way to test even-ness in a scalar, s,
isEven=false;
try, validateattributes(s,"numeric","even"); isEven=true; end,
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Howard Lam 2021 年 10 月 15 日

testN = 10000000;
testvar = round(rand(testN,1)*testN);
tic
output1=rem(testvar,2);
toc
tic
output2=floor(testvar/2) ~= testvar/2;
toc
tic
output3=bitget(testvar,1)==1;
toc
tic
output4 = (-1).^testvar == -1;
toc
The above produces the output
>> testisoddspeed
Elapsed time is 0.101100 seconds.
Elapsed time is 0.010721 seconds.
Elapsed time is 0.054311 seconds.
Elapsed time is 0.040362 seconds.
EDIT: Tested on AMD Ryzen 5800H 2018b. Updated answer for the case when your variables are already integers so that you do not have to cast first.
testN = 10000000;
testvar = round(rand(testN,1)*testN);
tic
output1=floor(testvar/2) ~= testvar/2;
toc
testvar = uint32(testvar);
tic
output2=rem(testvar,2)==1;
toc
tic
output3=bitget(testvar,1)==1;
toc
tic
output4 = (-1).^testvar == -1;
toc
results in
>> testisoddspeed
Elapsed time is 0.014634 seconds.
Elapsed time is 0.123930 seconds.
Elapsed time is 0.013089 seconds.
Elapsed time is 0.032953 seconds.
Bitget can be slightly faster.
##### 11 件のコメント表示非表示 10 件の古いコメント
Walter Roberson 2021 年 10 月 28 日
This is the code I used:
fprintf('1\n');
runtest();
fprintf('2\n');
runtest();
fprintf('3\n');
runtest();
function runtest();
testN = 10000000;
testvar = round(rand(testN,1)*testN);
tic
output1=mod(testvar,2);
toc
tic
output2=floor(testvar/2) ~= testvar/2;
toc
tic
output3=bitget(uint32(testvar),1);
toc
tic
output4 = (-1).^testvar == -1;
toc
end

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