# How to use spacing around operator?

조회 수: 4(최근 30일)
Spacing around the '+' operator gives unexpected results, in paritcular: a +b (space in front of - but not after the +). Where's the syntactical difference?
% simple example:
a=1
b=2
a+b % as expected
a + b % as expected
(a +b) % as expected
a +b % unexpected !

#### 댓글 수: 1

Stephen Cobeldick 3 Dec 2019

로그인 to comment.

### 답변 수 (3)

Walter Roberson 3 Dec 2019
Just like -5 is "unary minus", +5 is "unary plus". [a -b] is [a, -1*b] and [a +b] is [a, +1*b] -- except that uminus and uplus have actual associated functions, not just syntactic sugar . https://www.mathworks.com/help/matlab/ref/uplus.html
C = uplus(A) is an alternate way to execute +A, but is rarely used. It enables operator overloading for classes.

#### 댓글 수: 0

로그인 to comment.

Stephen Cobeldick 3 Dec 2019
This is explained in the MATLAB documentation:
And has also been covered several times on this forum, e.g.:
Really the differences between your examples come down to whether an operator can be both unary and binary (e.g. + and -) or is binary only (e.g. * and <):
1. If there is no space a unary operator has a higher priority than the binary.
2. If the operator is only binary then the space is always optional.
NOTE: All of the examples are code that should never be used in real life. Always use commas for separating elements of an array, if only because it makes the intention clear.

#### 댓글 수: 0

로그인 to comment.

Klaus Webers 3 Dec 2019
that solved my problem. Thanks a lot.
(as this "Zombi-problem" obviously comes up frequently, MathWorks should probably think about a more rigorous parsing at such instances. In particular, as the error message "Unrecognized function or variable 'a' " in may example case was misleading too.)

#### 댓글 수: 1

Walter Roberson 3 Dec 2019
It is using rigorous parsing: in every case where you have whitespace (or comma or beginning of an expression) followed by + or - followed by an expression, the + is unary plus, and the minus is unary minus.
The situation is exactly the same as [1 -2] meaning vertcat(1, uminus(2)) rather than vertcat(minus(1,2))
There are some contexts such as listing spin states where unary plus is common to see,
spin = [-1 -1 +1 +2 +1 -2 -1]
and that should not be treated as
spin = [-1, -1+1+2+1, -2, -1]
or
spin = [-1-1+1+2+1-2-1]

로그인 to comment.

이 질문에 답변하려면 로그인을(를) 수행하십시오.

Translated by