MATLAB: How to say if (A & B) or C in Matlab

if statement

Hi! I have three conditions A, B and C. I would like to set: if both A and B or C in Matlab. I thought to:

if (A && B) | C

but It doesn't work. How can i do it? Thanks!

Best Answer

| operates elementwise on arrays. You might want to check the size of A, B, and C. If then operates on the array (See @Stephen's answer).

>> help |
|   Logical or.
  A | B performs a logical or of arrays A and B and returns an array
  containing elements set to either logical 1 (TRUE) or logical 0
  (FALSE)....
    Note that there are two logical or operators in MATLAB.  The |
    operator performs an element-by-element or between matrices, while 
    the || operator performs a short-circuit or between scalar values.

I prefer using && and | | for a range of personal reasons:

Certainly when I was starting out, I didn't consider the possibility of the behavior of if operating on a vector. Keeping statements to the scalar operators adds implicit error-checking when you hand your code to someone else - they'll now get an error (&& doesn't operate on vectors) instead of a possibly ill-defined result. Of course, if you intend to operate on vectors, you can ignore this comment.
As @Stephen mentioned below, it doesn't have to evaluate the rest of the expression once the condition is met. Just make sure all of your () are in the right places.
It forces you to think a bit more about about the intent of the condition, for example do you want: all(A) to be true, or would you be happy if any(A) are true? Even though the default for "if all(A)" is equivalent to "if A", you've just made your intent explicitly clear.
People coming from other languages may interpret the intent differently. For example in python;

>> if [0, 0, 0]:
       print("yes")
>> yes

(because [0,0,0] is not None.) whereas;

>> if all([0, 0, 0]):
       print("yes")
>>

Related Solutions

MATLAB: & operator without if

The & operator is an elementwise operator. Just like the + operator will add corresponding elements of its inputs when given two vectors of the same size:

x = [1 2 3];
y = [4 5 6];
z = x + y % z(1) = x(1) + y(1), z(2) = x(2) + y(2), z(3) = x(3) + y(3)

The & operator will take the and of the corresponding elements of its inputs.

a = [true false true];
b = [true true false];
c = a & b; % c(1) = a(1) & b(1), c(2) = a(2) & b(2), c(3) = a(3) & b(3)

The & operator with two scalars as input returns true if both its inputs are non-zero and false otherwise.

[ true &  true; ... % true
  true & false; ... % false
 false &  true; ... % false
 false & false]     % false

MATLAB: What will be displayd and why

This is explained quite clearly in the if documentation: "An expression is true when its result is nonempty and contains only nonzero elements (logical or real numeric). Otherwise, the expression is false."

Which means:

[0,0,0,0] is false: all values are zero
[0,1,0,1] is false: some values are zero
~[0,0,0,0]=[1,1,1,1] is true: contains only nonzero elements
~[0,1,0,1]=[1,0,1,0] is false: some values are zero

Note that the definition defines a true expression as "contains only nonzero elements" but does not give an upper-limit to the number of nonzero elements.

Best Answer

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MATLAB: & operator without if

MATLAB: What will be displayd and why

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