# Testing Matlab Arrays for Equality.

Testing a matlab array for equality can be doen a few different was some have surprising side effects if your not use to working with vectorised testing.

Initial test :

```
a = [1,2,3];
if (a == [1,2,3])
disp('equal')
end
> equal
```

Seems easy, But what happens if the dimensions of the array are incorrect?

```
a = [1,2,3];
if (a == [1,2,3,4])
disp('equal')
end
Error using ==
Matrix dimensions must agree
```

May be if we check dimensions first using short-circuiting (`&&`

) operators. NB: Short circuiting operators only execute if required, if it failed on the left hand side the right side will not be evaluated.

```
a = [1,2,3];
if ((length(a) == 4) && (a == [1,2,3,4]))
disp('equal')
end
```

So far so good, but lets check it will also pass:

```
a = [1,2,3];
if ((length(a) == 3) && (a == [1,2,3]))
disp('equal')
end
Operands to the || and && operators must be convertible to logical scalar
values.
```

This is where it got interesting for me:

```
a ==[1,2,3]
ans =
1 1 1
```

The basic equality `==`

test for arrays is vectorised. When this is the only test it gets reduced down to true or false, but can not be combined with scalars.

Then I the discovered the isequal function.

```
a = [1,2,3];
isequal(a, [1,2,3])
ans =
1
a = [1,2,3];
isequal(a, [1,2,3,4])
ans =
0
```

For direct comparisons of arrays use `isequal(a,b)`

for vectorised operations use `a==b`

.

Matlab

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