Different result when adding variables

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

Answer 1

[Stephen23]

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...

[Jim]

I just thought the colon operator had priority over the plus operator...

Summary: always use parentheses to be sure, especially if you are programming in different languages

[Steven Lord]

To elaborate slightly on Stephen's answer, the plus operator is at precedence level 6 while the colon operator is at level 7.