# Sample Uncertain Elements to Create Arrays

A common way to generate an array is to sample the uncertain elements of an uncertain object. This example shows how to generate arrays by taking random samples of a `umat` uncertain matrix that has two uncertain elements. (To generate arrays by sampling at specific values, use `usubs`.)

Create an uncertain matrix.

```a = ureal('a',4); b = ureal('b',2); M = [a b;b*b a/b;1-b 1+a*b]```
```M = Uncertain matrix with 3 rows and 2 columns. The uncertainty consists of the following blocks: a: Uncertain real, nominal = 4, variability = [-1,1], 3 occurrences b: Uncertain real, nominal = 2, variability = [-1,1], 6 occurrences Type "M.NominalValue" to see the nominal value, "get(M)" to see all properties, and "M.Uncertainty" to interact with the uncertain elements. ```

Sample the uncertain real parameter `b` in the matrix `M`, at 20 random points within its range.

`[Ms,bvalues] = usample(M,'b',20);`

This results in an array of 20 3-by-2 `umat` matrices, with only one uncertain element, `a`. The uncertain element `b` of `M` has been sampled out, leaving a new array dimension in its place.

`Ms`
```Ms = 20x1 array of uncertain matrices with 3 rows, 2 columns, and the following uncertain blocks: a: Uncertain real, nominal = 4, variability = [-1,1], 3 occurrences Type "Ms.NominalValue" to see the nominal value, "get(Ms)" to see all properties, and "Ms.Uncertainty" to interact with the uncertain elements. ```

Additionally, `bvalues` is a structure containing the corresponding sampled values of `b`.

`bvalues`
```bvalues=20×1 struct array with fields: b ```

Next, sample the remaining uncertain real parameter `a` in the matrix `Ms`. This removes the second uncertain block, resulting in a 3-by-2-by-20-by-15 `double`.

```[Mss,avalues] = usample(Ms,'a',15); size(Mss)```
```ans = 1×4 3 2 20 15 ```

You can also sample multiple parameters at once. The following operation returns `Mss1`, which is identical to `Mss`.

`[Mss1,values] = usample(M,'b',20,'a',15);`

Rather than sampling each variable (`a` and `b`) independently, generating a 20-by-15 grid in a 2-dimensional space, you can sample the two-dimensional space directly. Sample the 2-dimensional space with 800 points.

`[Ms2d,values] = usample(M,{'a' 'b'},800);`

`Ms2d` is a 3-by-2-by-800 `umat` array, where each entry corresponds to a different randomly selected `(a,b)` pair. The structure array `values` contains these `(a,b)` values.

`values`
```values=800×1 struct array with fields: a b ``` 