MATLAB: How to code “if (a and b) or (c and d)”

conditionalsMATLAB

I'm writing a code where I need a conditional statement something like the following:

x = 1;
y = 2;
if (((x || y == 1) && (x || y == 3))) || (((x || y == 2) && (x || y == 3))
  fprintf('true');
else
fprintf('false');
end;

I tried this, but it keeps outputting "true", when I want it to output "false". I want it to say "If (x or y is 1) and (x or y is 3), or if (x or y is 2) and (x or y is 3), then…". But that clearly isn't what this is saying. Please help!

Best Answer

This does not do what you want (because you are not comparing x with anything, so MATLAB treats the x as true if it is non-zero):

 if (((x || y == 1) && ...

You have to compare x first, then perform the or operation:

 if (((x==1 || y==1) && ...

You can try this yourself:

>> (3 || 2==4) % 3 is non-zero, treated as true, therefore output is true
ans =  1
>> (3==4 || 2==4) % test if 3==4 and 2==4
ans = 0

Related Solutions

MATLAB: How to use not equal to ‘~=’ operator in if statement

A problem of elementary logic?

You want an error to return only if A is not in the set {'A','B'}. So a call to ismember might be a good alternative.

Regardless, given the approach you have followed, if x is equal to 'A', then the second half of the clause will be true, even though the first part of the clause is false. And the logical statement

   false || true

is TRUE.

You are asking for a result that is only true when BOTH parts of the clause are true. Use a logical and, NOT a logical or.

if(x~='A') && (x~='B')

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

Best Answer

Related Solutions

MATLAB: How to use not equal to ‘~=’ operator in if statement

MATLAB: & operator without if

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