MATLAB: Different result when adding variables

MATLABvariables

This is in MATLAB R2016a. The addition
1:3 + [0 0 5]
gives
1 2 3
if we assign
x = 1:3;
and
y = [0 0 5];
then x+y is
 1 2 8

Best Answer

You are doing two different operation sequences, so why the surprise that you get two different results?
First Case
>> 1:3 + [0 0 5]
ans =
 1   2   3
because of the operator precedence (plus is higher than colon) is equivalent to
>> 1: (3 + [0 0 5])
ans =
 1   2   3
which is equivalent to
>> 1:[3,3,8]
ans =
 1   2   3
and thus is just
>> 1:3
ans =
 1   2   3
because the colon operator only uses the first element of the vector and ignore the rest: "If you specify nonscalar arrays, MATLAB interprets j:i:k as j(1):i(1):k(1)."
Second Case
 >> x = 1:3;
 >> y = [0 0 5];
 >> x+y
 ans =
   1   2   8
performs an element-wise addition on two vectors.
Summary
Beginners often forget about operator precedence and to read the documentation...
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