how to find out if a number is even or not

조회 수: 1,297(최근 30일)
divya r
divya r 2012년 10월 23일
댓글: Walter Roberson 2021년 10월 28일
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?
  댓글 수: 3
Steven Lord
Steven Lord 2020년 10월 9일
So Inf is even?
>> s = (-1)^Inf
s =
1
How about NaN?
>> 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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채택된 답변

Walter Roberson
Walter Roberson 2012년 10월 23일
편집: MathWorks Support Team 2018년 11월 9일
See mod and rem
  댓글 수: 1
Dillen.A
Dillen.A 2020년 2월 5일
편집: Dillen.A 2020년 2월 5일
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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추가 답변(8개)

Jan
Jan 2012년 10월 23일
Care for exceptions:
NaN, Inf, 1e54, int8(-128)
There are some FEX submission for this task, e.g. FEX: parity checker.

luis fonseca
luis fonseca 2020년 10월 9일
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
  댓글 수: 2
Howard Lam
Howard Lam 2021년 10월 15일
use .^

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Matt J
Matt J 2012년 10월 23일
if bitget(A,1) %odd
else %even
end
  댓글 수: 2
Josh Meyer
Josh Meyer 2018년 10월 10일
편집: Josh Meyer 2018년 10월 10일
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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Ibn e Adam
Ibn e Adam 2020년 2월 18일
% 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
  댓글 수: 4
Matt J
Matt J 2020년 2월 26일
not in inverted commas
I guess inverted commas = single quotes

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Anmol  singh
Anmol singh 2020년 4월 10일
편집: Anmol singh 2020년 4월 10일
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;
  댓글 수: 1
Walter Roberson
Walter Roberson 2020년 4월 10일
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
Matt J 2020년 10월 9일
편집: Matt J 2020년 10월 9일
One more way to test even-ness in a scalar, s,
isEven=false;
try, validateattributes(s,"numeric","even"); isEven=true; end,

Howard Lam
Howard Lam 2021년 10월 15일
편집: Howard Lam 2021년 10월 27일
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.
  댓글 수: 11
Walter Roberson
Walter Roberson 2021년 10월 28일
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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