Integers in Arrays Give Strange Result

2 views (last 30 days)
For example, try this,
vec = [pi, -2, uint8(1)]
vec =
1×3 uint8 row vector
3 0 1
vec = [pi, uint16(2), int8(-2)]
vec =
1×3 uint16 row vector
3 2 0
vec = [pi, uint16(2), int16(-2)]
vec =
1×3 uint16 row vector
3 2 0
So, if one element is an integer MATLAB seem to cast every other element in the array to that integer class. If there are several integer elements all elements seem to be cast to the higher integer class and, in a draw, to the unsigned class.
This is an extremely odd behavior. One would expect all elements to be cast to a numeric class that can accurately represent all elements or, at least, all elements cast to 'double' if there are mixed numerical classes in the array.
This can lead to totally wrong results if a user supplies integers to a function, for example this one,
function y = myFun(x, k)
par = [k, -2];
y = par(1) + par(2)*cos(x);
end
myFun(0, 1) will give -1 and myFun(0, uint8(1)) will give the incorrect result 1.
So, is there some logic behind this behavior or is it a bug?

Accepted Answer

Steven Lord
Steven Lord on 15 Nov 2022
For concatenation see this documentation page. If you concatenate one or more integer arrays with one or more double arrays, the leftmost of the integer arrays will determine the type of the result.
For the behavior of arithmetic see this documentation page.
This is the documented behavior and has been for many years. It is not a bug.
  7 Comments
Paul
Paul on 15 Nov 2022
Looking at M2 in Bruno's example and the doc page linked by the cyclist, the leftmost integer type governs, not the signedness nor smallest [number of bits] type when concatenating doubles with integer types, IIUC.

Sign in to comment.

More Answers (0)

Products


Release

R2020a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!