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# for (drange)

`for`-loop over distributed range

## Syntax

```for `variable` = drange(`colonop`)
statement
...
statement
end
```

## Description

The general format is

```for variable = drange(colonop) statement ... statement end```

The `colonop` is an expression of the form `start:increment:finish` or `start:finish`. The default value of increment is 1. The `colonop` is partitioned by `codistributed.colon` into `numlabs` contiguous segments of nearly equal length. Each segment becomes the iterator for a conventional for-loop on an individual worker.

The most important property of the loop body is that each iteration must be independent of the other iterations. Logically, the iterations can be done in any order. No communication with other workers is allowed within the loop body. The functions that perform communication are `gop`, `gcat`, `gplus`, `codistributor`, `codistributed`, `gather`, and `redistribute`.

It is possible to access portions of codistributed arrays that are local to each worker, but it is not possible to access other portions of codistributed arrays.

The `break` statement can be used to terminate the loop prematurely.

## Examples

Find the rank of magic squares. Access only the local portion of a codistributed array.

```r = zeros(1, 40, codistributor()); for n = drange(1:40) r(n) = rank(magic(n)); end r = gather(r);```

Perform Monte Carlo approximation of pi. Each worker is initialized to a different random number state.

```m = 10000; for p = drange(1:numlabs) z = rand(m,1) + i*rand(m,1); c = sum(abs(z) < 1) end k = gplus(c) p = 4*k/(m*numlabs);```

Attempt to compute Fibonacci numbers. This will not work, because the loop bodies are dependent.

```f = zeros(1, 50, codistributor()); f(1) = 1; f(2) = 2; for n = drange(3:50) f(n) = f(n-1) + f(n-2) end```

## See Also

Introduced in R2007b

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