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# error in resultes of "OR" operator

Asked by Aseel H on 29 Jun 2013

in the following code I need subtract the values 255 and 254 by 1

and adding the value 0 and 1 by 1 and the other values don't change

```    X=[255 250 0 100 38 47 150 254
253 251 250 0 0 47 25 252
0 0 0 90 145 74 30 249
200 220 0 1 2 3 225 4
0 255 251 0 4 20 35 245
255 250 0 100 38 47 150 254
200 220 0 1 2 3 225 4
253 251 250 0 0 47 25 252];```
```    Max = 255;
Min = 0;
[x,y] = size(X);```
```    for i= 1:x
for j = 1:y
if X(i,j)==(Max | Max-1)
X1(i,j) = X(i,j)-1;
elseif X(i,j)== (Min | Min+1)
X1(i,j) = X(i,j)+1;
else
X1(i,j)= X(i,j);
end
end
end```

**************************************

but resultes not change:it give me

```    X1=[255 250 0 100 38 47 150 254
253 251 250 0 0 47 25 252
0 0 0 90 145 74 30 249
200 220 0 1 2 3 225 4
0 255 251 0 4 20 35 245
255 250 0 100 38 47 150 254
200 220 0 1 2 3 225 4
253 251 250 0 0 47 25 252];```

Please....I need know what error in the code

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Answer by the cyclist on 29 Jun 2013

You have a syntax problem when you try to do

```X(i,j)==(Max | Max-1)
```

because that is not going to check whether X(i,j) is in a set. That is valid MATLAB syntax, but it is not doing what you think it is. You might want to read the documentation for the or() function to see exactly what it does:

```doc or
```

Instead, I think you want the syntax

```if (X(i,j)==Max) | (X(i,j)==(Max-1))
```

You could also use

```if ismember(X(i,j),[Max Max-1])
```

Finally, note that you can do this operation on the entire matrix at once:

```X1 = X;
idxHi = ismember(X,[255,254])
X1(idxHi) = X(idxHi)-1;
```
```idxLo = ismember(X,[0,1])
X1(idxLo) = X(idxLo)+1;
```

Answer by Walter Roberson on 29 Jun 2013
```X(i,j)== (Min | Min+1)
```

means to evaluate the logical condition (Min | Min+1) and then compare that logical result to what is in X(i,j).

Try

```if X(i,j) == Min | X(i,j) == Min+1
```