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title = "Execute simulations batches" | ||
title = "Parameter Sweeping with simulation batches" | ||
weight = 1 | ||
tags = ["batch", "variables", "dry"] | ||
summary = "Execute multiple instances of the same configuration" | ||
summary = "Execute multiple instances of a simulation with different parameters" | ||
+++ | ||
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In some cases you may need to test the same simulation configuration | ||
with different *parameters*. Suppose for example that you want to see what | ||
happens when you place a bunch of pedestrian in a circle | ||
(for sake of semplicity we'll ignore their behavior). You may want to | ||
(for sake of semplicity we'll ignore their behavior). | ||
You may want to | ||
observe the scenario with 50 pedestrians placed in a 5 meters radius circle. | ||
Then you may like to observe it with 100 pedestrian and perhaps by changing | ||
the circle radius also. Instead of re-writing the configuration file over-and-over | ||
for each parameter combination, Alchemist offers the possibility to write the | ||
configuration once, and it will then derive a batch of simulations. | ||
configuration once, and it will then derive a batch of simulations.the same configuration | ||
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## Launching batch simulations | ||
To exploit this mechanism, you must declare what we above called "parameters" | ||
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To exploit this mechanism, you must declare the "parameters" | ||
as **variables**. In our example, they would be the *number of pedestrian* and | ||
the *radius of the circle* where to place them. Let's write the configuration file, | ||
specifing that we want to test the simulation with 10, 30, 50, 70, 90 pedestrian | ||
specifing that we want to test the simulation with 10, 30, 50, 70, 90 pedestrians | ||
and a 5, 10, 15 meters circle radius: | ||
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{{< code path="src/test/resources/website-snippets/batch-pedestrian-simulation.yml" >}} | ||
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{{% notice info %}} | ||
To understand how variables work refer to [this page](/howtos/simulation/variables/). | ||
You may also want to learn how to deal with [data exportation](/howtos/simulation/export/) | ||
and [termination criterias](/howtos/execution/termination/). | ||
You may also want to learn how to [export data](/howtos/simulation/export/) | ||
and specifying [termination criteria](/howtos/execution/termination/). | ||
{{% /notice %}} | ||
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Now we can launch the batch of simulations by yielding the following command: | ||
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```bash | ||
./gradlew run --args="-y <path-to-simulation> -b -hl -var pedestrianNumber - var circleRadius -e <export-path>" | ||
``` | ||
Now we can launch the batch of simulations by providing the simulator the following command-line arguments: | ||
* `-b`: enable batch mode | ||
* `-var pedestrianNumber`: all values of variable `pedestrianNumber` will be tested | ||
* `-var circleRadius`: all values of variable `circleRadius` will be tested | ||
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The `-b` option is to tell Alchemist that we want to execute a batch, while the `-hl` stands | ||
for headless which means we are not interested in starting-up a gui. | ||
Under the hood the simulator will compute the cartesian product of the variables sets | ||
specified with the `-var` option. | ||
Under the hood, the simulator will compute the cartesian product of the all possible values of the variables selected with the `-var` option. | ||
Variables not selected for the batch will have their default value. |