# Loop constructs

Gretl Manual: Gnu Regression, Econometrics and Time-series Library
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# Chapter 10. Loop constructs

# Introduction

The command `loop` opens a special mode in which `gretl` accepts a block of commands to be repeated one or more times. This feature is designed for use with Monte Carlo simulations, bootstrapping of test statistics, and iterative estimation procedures. The general form of a loop is:

          loop control-expression [ --progressive | --verbose ]
             loop body
          endloop

Five forms of `control-expression` are available, as explained below. In the `loop body` the following commands are accepted: `genr`, `ols`, `print`, `printf`, `pvalue`, `sim`, `smpl`, `store`, `summary`, `if`, `else` and `endif`.

By default, the `genr` command operates quietly in the context of a loop (without printing information on the variable generated). To force the printing of feedback from `genr` you may specify the `--verbose` option to `loop`.

The `--progressive` option to `loop` modifies the behavior of the commands `ols`, `print` and `store` in a manner that may be useful with Monte Carlo analyses (see the Section called Progressive mode).

The following sections explain the various forms of the loop control expression and provide some examples of use of loops.

> Tip: If you are carrying out a substantial Monte Carlo analysis with many thousands of repetitions, memory capacity and processing time may be an issue. To minimize the use of computer resources, run your script using the command-line program, `gretlcli`, with output redirected to a file.

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Numerical accuracy |  | Loop control variants