This is A PREVIEW for NEST 3.0 and NOT an OFFICIAL RELEASE! Some functionality may not be available and information may be incomplete!

Write data to plain text files

The ascii recording backend writes collected data persistently to a plain text ASCII file. It can be used for small to medium sized simulations, where the ease of a simple data format outweighs the benefits of high-performance output operations.

This backend will open one file per recording device per thread on each MPI process. This can cause a high load on the file system in large simulations. This backend can become prohibitively inefficient, particularly on machines with distributed filesystems. In case you experience such scaling problems, the recording backend for SIONlib may be a possible alternative.

Filenames of data files are determined according to the following pattern:


The properties data_path and data_prefix are global kernel properties. They can, for example, be set during repetitive simulation protocols to separate the data originating from individual runs. The label replaces the model name component if it is set to a non-empty string. node_id and vp denote the zero-padded global ID and virtual process of the recorder writing the file. The filename ends in a dot and the file_extension.

The life of a file starts with the call to Prepare and ends with the call to Cleanup. Data that is produced during successive calls to Run in between a pair of Prepare and Cleanup calls will be written to the same file, while the call to Run will flush all data to the file, so it is available for immediate inspection.

When creating a new recording, if the file name already exists, the Prepare call will fail with a corresponding error message. To instead overwrite the old file, the kernel property overwrite_files can be set to true using SetKernelStatus. An alternative way for avoiding name clashes is to re-set the kernel properties data_path or data_prefix, so that another filename is chosen.

Data format

Any file written by the ascii recording backend starts with an informational header. The first header line contains the NEST version, with which the file was created, followed by the version of the recording backend in the second. The third line describes the data by means of the field names for the different columns. All lines of the header start with a # character.

The first field of each record written is the node ID of the neuron the event originated from, i.e., the source of the event. This is followed by the time of the measurement, the recorded floating point values and the recorded integer values.

The format of the time field depends on the value of the property time_in_steps. If set to false (which is the default), time is written as a single floating point number representing the simulation time in ms. If time_in_steps is true, the time of the event is written as a pair of values consisting of the integer simulation time step in units of the simulation resolution and the negative floating point offset in ms from the next integer grid point.


The number of decimal places for all decimal numbers written can be controlled using the recorder property precision.

Parameter summary


A string (default: “dat”) that specifies the file name extension, without leading dot. The generic default was chosen, because the exact type of data cannot be known a priori.


A list of the filenames where data is recorded to. This list has one entry per local thread and is a read-only property.


A string (default: “”) that replaces the model name component in the filename if it is set.


An integer (default: 3) that controls the number of decimal places used to write decimal numbers to the output file.


A Boolean (default: false) specifying whether to write time in steps, i.e., in integer multiples of the simulation resolution plus a floating point number for the negative offset from the next grid point in ms, or just the simulation time in ms. This property cannot be set after Simulate has been called.