# Tagging constraints

When a list of constraints is generated, it is sometimes hard to remember which constraints model what, which can cause problems if you need to debug or for some reason look at the constrants. To alleviate this problem, you can tag your list of constraints easily with descriptions.

The syntax is very easy, simply add a : followed by a string.

```
sdpvar x
Constraints = [x>=0]:'Positivity'
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| ID| Constraint| Type| Tag|
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| #1| Numeric value| Element-wise 1x1| Positivity|
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
```

This tagging can be used also inside a list of constraints, but due to the order of evaluation in MATLAB, it is important to add parentheses around the constraints.

```
sdpvar x
Constraints = [(x>=0):'Positivity',(x=<1):'Bounded']
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| ID| Constraint| Type| Tag|
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| #1| Numeric value| Element-wise 1x1| Positivity|
| #2| Numeric value| Element-wise 1x1| Bounded|
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
```

Alternatively, use brackets.

```
sdpvar x
Constraints = [[x>=0]:'Positivity', [x<=1]:'Bounded']
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| ID| Constraint| Type| Tag|
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| #1| Numeric value| Element-wise 1x1| Positivity|
| #2| Numeric value| Element-wise 1x1| Bounded|
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
```

The tag is useful not only for displays, but can also be used as an index.

```
Constraints('Bounded')
+++++++++++++++++++++++++++++++++++++++++++++++++++++++
| ID| Constraint| Type| Tag|
+++++++++++++++++++++++++++++++++++++++++++++++++++++++
| #1| Numeric value| Element-wise 1x1| Bounded|
+++++++++++++++++++++++++++++++++++++++++++++++++++++++
```

Add an index too in case needed

```
x = sdpvar(5,1);
Constraints = [];
for i = 1:5
Constraints = [Constraints, (x(i) >= 0):['Cool iteration ' num2str(i)]];
end
Constraints
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| ID| Constraint| Tag|
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| #1| Element-wise inequality 1x1| Cool iteration 1|
| #2| Element-wise inequality 1x1| Cool iteration 2|
| #3| Element-wise inequality 1x1| Cool iteration 3|
| #4| Element-wise inequality 1x1| Cool iteration 4|
| #5| Element-wise inequality 1x1| Cool iteration 5|
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
```