Round to nearest odd integer

Does MATLAB have a function to round numbers to the nearest odd integer?

[Walter Roberson]

Do you want negative numbers handled the same way? e.g., -1/3 rounded to -1 ?

Answer 1

[Matt Fig]

I don't think so, but you could make your own:

function S = round_odd(S)
% round to nearest odd integer.
idx = mod(S,2)<1;
S = floor(S);
S(idx) = S(idx)+1;

[Sean de Wolski]

I think you meant:

idx = mod(S,2)<1 %note < not <=

Otherwise it returns evens for S = magic(5);

[Matt Fig]

Yeah, I caught that one too. I like Babak's better anyway, LOL.

Answer 2

[Babak]

Not that I know of.. but you can use this:

function y=fun(x)
y = 2*floor(x/2)+1;
end

depending on what you want to do with the even numbers you can ether use floor or ceil in the above function.

[mirza]

That's an efficient approach, but its better to use "round" function instead of "floor" or "ceiling" function. In floor case, the error may occur for rounding numbers to Even.

For example.

If the number is " 23.7227731 "

then statement => 2*floor(x/2) will provide answer "22"

However,

the statement => 2*round(x/2) will provide answer "24"

[Walter Roberson]

2*floor(23.7227731/2)+1 would be 23, and 23.7227731 has indeed been rounded to the nearest odd number.

2*round(23.7227731/2)+1 would be 25, but 25-23.7227731 is about 1.67 which is greater than 23.7227731-23 ~= 0.72 . Therefore 23 is the closest odd number, to 23.722773, and 25 is not the closest odd number.

I would therefore suggest to you that round() does not solve the problem posed by the original poster.

Answer 3

[Azzi Abdelmalek]

   a=7.8; %example

   round((a-1)/2)*2+1

[Roger Luna]

... And for the nearest even integer:

    a=7.8; %example

    round((a-2)/2)*2+2

[mirza]

True, the function "round" is better option instead of functions "floor" or "ceiling" as suggested in thread. In floor case, the error may occur for rounding numbers to Even.

For example.

If the number is " 23.7227731 "

then statement => 2*floor(x/2) will provide answer "22"

However,

the statement => 2*round(x/2) will provide answer "24"

[Walter Roberson]

See https://www.mathworks.com/matlabcentral/answers/45932-round-to-nearest-odd-integer#comment_781808 for an explanation of why using round() would be incorrect.

Answer 4

[gerit]

x-mod(x,2)+1

even numbers will be rounded up

Answer 5

[Gimantha Upasena]

In matlab what is the method to take the values of a matrix and round them off to the nearest even number?..... meaning 2.1 should be rounded off to 2 and also 2.8 should also be rounded off to 2 because if rounded off to 3 ...3 is an odd number so it's not accepted.

[Walter Roberson]

floor(x/2)*2

which should work for both positive and negative numbers.