log2() only works with double types?

log2() seems to only work with 'double' types. It throws error when argument is int64.

num = 10000;
d = floor(num / 7);

a = log2(d);
disp(a);

   10.4798

d = int64(num / 7);
b = log2(double(d));
disp(b);

   10.4808

b = log2(d);

Check for incorrect argument data type or missing argument in call to function 'log2'.

disp(b);

Answer 1

[Simon Chan]

Check MATLAB documentation and this fucntion log2 supports type single or double as the input argument type.

[atharva aalok]

This is surprising. I would expect it to work for different int types. Why should the user keep track of such details?

I don't see a problem with it working for different int types.

Why is it so, any clues?

[Steven Lord]

The output of the log2 function is the same type as the input. [This is a general pattern for many element-wise functions.] There are only a handful of int64 numbers whose base 2 log is representable as an int64 number. If it were defined for int64 we'd likely have a lot of people complaining about "bugs" in log2 when it was returning the correct answer just not the answer they expected.

log2Int64 = @(x) int64(log2(double(x)));
x = int64(10:20);
y = log2Int64(x)

y = 1×11

3 3 4 4 4 4 4 4 4 4 4

check = x - 2.^y % Is this what you would expect?

ans = 1×11

2 3 -4 -3 -2 -1 0 1 2 3 4

[atharva aalok]

That was great help Steven! Thanks a ton!