# Specify Start Points for `MultiStart`, Problem-Based

When solving a problem using `MultiStart` in the problem-based approach, you can specify the start points using one or both of these techniques:

• Create a vector of `OptimizationValues` objects using the `optimvalues` function. Pass this vector as the `x0` argument to `solve`.

• Set the `MinNumStartPoints` name-value argument when you call `solve`. If `MinNumStartPoints` exceeds the number of points in `x0`, then `solve` creates extra points at random within the problem bounds.

### Vector of Initial Points

For this example, create the initial points vector as a grid for the variable `x` consisting of integer values from –10 through 10, and for the variable `y` consisting of half-integer values from `–5/2` through `5/2`. The `optimvalues` function requires a problem, so create an optimization problem with the objective function `peaks(x,y)`.

You must specify the points for `optimvalues` so that the dimension (index) of the number of points is last. For example, to give multiple values of a scalar `t` with `n` points, specify

$\left[t\left(1\right)\phantom{\rule{0.5em}{0ex}}t\left(2\right)\phantom{\rule{0.5em}{0ex}}...\phantom{\rule{0.5em}{0ex}}t\left(n\right)\right]$ (This is 1-by-`n`, and `n` is the last index.)

To give multiple values of a vector variable `w` of length 2, specify

$\left[\begin{array}{ccccc}w\left(1,1\right)& w\left(1,2\right)& w\left(1,3\right)& \cdots & w\left(1,n\right)\\ w\left(2,1\right)& w\left(2,2\right)& w\left(2,3\right)& \cdots & w\left(2,n\right)\end{array}\right]$ (This is 2-by-`n`, and `n` is the last index.)

This rule holds even for row vectors. In other words, you specify multiple row vectors as if each were a column vector.

To give multiple values of a matrix `A` that is 2-by-3, specify

$\left[\begin{array}{ccc}\mathit{A}\left(1,1,1\right)& \mathit{A}\left(1,2,1\right)& \mathit{A}\left(1,3,1\right)\\ \mathit{A}\left(2,1,1\right)& \mathit{A}\left(2,2,1\right)& \mathit{A}\left(2,3,1\right)\end{array}\right]\left[\begin{array}{ccc}\mathit{A}\left(1,1,2\right)& \mathit{A}\left(1,2,2\right)& \mathit{A}\left(1,3,2\right)\\ \mathit{A}\left(2,1,2\right)& \mathit{A}\left(2,2,2\right)& \mathit{A}\left(2,3,2\right)\end{array}\right]\cdots \left[\begin{array}{ccc}\mathit{A}\left(1,1,\mathit{n}\right)& \mathit{A}\left(1,2,\mathit{n}\right)& \mathit{A}\left(1,3,\mathit{n}\right)\\ \mathit{A}\left(2,1,\mathit{n}\right)& \mathit{A}\left(2,2,\mathit{n}\right)& \mathit{A}\left(2,3,\mathit{n}\right)\end{array}\right]$(This is 2-by-3-by-`n`, and `n` is the last index.)

In the present example, ensure that you specify the multiple values of the scalar variables `x` and `y` as row vectors, as in the scalar `t` example.

```x = optimvar("x",LowerBound=-10,UpperBound=10); y = optimvar("y",LowerBound=-5/2,UpperBound=5/2); prob = optimproblem(Objective=peaks(x,y)); xval = -10:10; yval = (-5:5)/2; [x0x,x0y] = meshgrid(xval,yval); % Convert x0x and x0y to row vectors for optimvalues x0 = optimvalues(prob,x=x0x(:)',y=x0y(:)');```

Solve the minimization problem starting from all the points in `x0`.

```ms = MultiStart; [sol,fval,eflag,output] = solve(prob,x0,ms)```
```Solving problem using MultiStart. MultiStart completed the runs from all start points. All 231 local solver runs converged with a positive local solver exitflag. ```
```sol = struct with fields: x: 0.2283 y: -1.6255 ```
```fval = -6.5511 ```
```eflag = LocalMinimumFoundAllConverged ```
```output = struct with fields: funcCount: 2230 localSolverTotal: 231 localSolverSuccess: 231 localSolverIncomplete: 0 localSolverNoSolution: 0 message: 'MultiStart completed the runs from all start points. ...' local: [1x1 struct] objectiveDerivative: "reverse-AD" constraintDerivative: "closed-form" globalSolver: 'MultiStart' solver: 'fmincon' ```

### Random Start Points

Solve the problem again, this time using `MultiStart` from 25 random initial points. Set the initial point for `solve` to `[–1,2]`.

```init.x = -1; init.y = 2; rng default % For reproducibility [sol2,fval2,eflag2,output2] = solve(prob,init,ms,MinNumStartPoints=25)```
```Solving problem using MultiStart. MultiStart completed the runs from all start points. All 25 local solver runs converged with a positive local solver exitflag. ```
```sol2 = struct with fields: x: 0.2283 y: -1.6255 ```
```fval2 = -6.5511 ```
```eflag2 = LocalMinimumFoundAllConverged ```
```output2 = struct with fields: funcCount: 161 localSolverTotal: 25 localSolverSuccess: 25 localSolverIncomplete: 0 localSolverNoSolution: 0 message: 'MultiStart completed the runs from all start points. ...' local: [1x1 struct] objectiveDerivative: "reverse-AD" constraintDerivative: "closed-form" globalSolver: 'MultiStart' solver: 'fmincon' ```

This time, `MultiStart` runs from 25 pseudorandom initial points. The solution is the same as before.