# Matrix Simple Index Question

Asked by Steve on 1 Jun 2012
Latest activity Commented on by Steve on 2 Jun 2012

Hello Experts,

1) Given matrix A with m rows and n columns, I want to check if there is an entry A(i,j)>alpha and if yes to make it A(i,j) = beta. How to make it without for and if? 2) How to make it in a vector of size (1,m) or (1,n)?

## Products

Answer by Oleg Komarov on 1 Jun 2012

Sample inputs:

```m = 10;
n =  13;
A = rand(m,n);
alpha = .38;
```

Use logical indexing

```idx = A > alpha;
A(idx) = 10;
```

Same applies to a vector (just play around with m and n to see that).

Oleg Komarov on 1 Jun 2012

Check out the getting started guide and especially this section: http://www.mathworks.co.uk/help/techdoc/learn_matlab/f2-8955.html

Oleg Komarov on 1 Jun 2012

Demos are also useful: http://www.mathworks.co.uk/products/matlab/demos.html

Steve on 2 Jun 2012

Dear Oleg, again thank you very very much!!!
It was my great pleasure to get your answer and experts guide!
Steve