Adding array create via colon operator.

In cleaning up some code, the editor identified some supposedly unnecessary brackets that turned out to be completely necessary (at least parentheses). However, removing them gave some unexpected results. I was wonder if anyone had an explanation for the following example or is it a bug? FYI, I am using Matlab 2011a.

>> x = [1 2 3 4];
>> y = x + [1:4]  %with brackets
y =
     2     4     6     8

>> y = x + 1:4  %w/o brackets or parentheses
y =
     2     3     4

Granted parentheses also work correctly in the first equation ... However, why is the 2nd output only 3 elements? What is Matlab actually doing in that example?

Thanks,

Answer 1

[Sean de Wolski]

It's grouping it like this:

(x+1):2

Best practice is to always use parenthesis! So for your example

x + (1:4)

The []s are unnecessary here because they are horizontally concatenating the vector that is already a row vector (the same as [1 2 pi]). Parenthesis don't specify concatenation but do specify order of operations.

[Ben]

Thanks! That does appear to be what it is doing. I could not see how it was coming up that 3 element answer.