# Command: noise_generator

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Name:

    noise_generator - Device to generate Gaussian white noise current.

Description:

      This device can be used to inject a Gaussian "white" noise current into a node.
      The current is not really white, but a piecewise constant current with Gaussian
      distributed amplitude. The current changes at intervals of dt. dt must be a
      multiple of the simulation step size, the default is 1.0ms,
      corresponding to a 1kHz cut-off.
      Additionally a second sinusodial modulated term can be added to the standard
      deviation of the noise.

      The current generated is given by

      I(t) = mean + std * N_j  for t_0 + j dt <= t < t_0 + (j-1) dt

      where N_j are Gaussian random numbers with unit standard deviation and t_0 is
      the device onset time.
      If the modulation is added the current is given by

      I(t) = mean + sqrt(std^2 + std_mod^2 * sin(omega * t + phase)) * N_j
      for t_0 + j dt <= t < t_0 + (j-1) dt

      For a detailed discussion of the properties of the noise generator, please see
      the noise_generator.ipynb notebook included in the NEST source code
      (docs/model_details).

Parameters:

      The following parameters can be set in the status dictionary:

      mean	 double	- mean value of the noise current in pA
      std	 double	- standard deviation of noise current in pA
      dt	 double	- interval between changes in current in ms, default 1.0ms
      std_mod   double	- modulated standard deviation of noise current in pA
      phase	 double	- Phase of sine modulation (0-360 deg)
      frequency double	- Frequency of sine modulation in Hz

Sends:

    CurrentEvent

Remarks:

     	- All targets receive different currents.
     	- The currents for all targets change at the same points in time.
     	- The interval between changes, dt, must be a multiple of the time step.
     	- The effect of this noise current on a neuron DEPENDS ON DT. Consider
      the membrane potential fluctuations evoked when a noise current is
      injected into a neuron. The standard deviation of these fluctuations
      across an ensemble will increase with dt for a given value of std.
      For the leaky integrate-and-fire neuron with time constant tau_m and
      capacity C_m, membrane potential fluctuations Sigma at times t_j+delay are
      given by

      Sigma = std * tau_m / C_m * sqrt( (1-x) / (1+x) ) where x = exp(-dt/tau_m)

      for large t_j. In the white noise limit, dt -> 0, one has

      Sigma -> std / C_m * sqrt(dt * tau / 2).

      To obtain comparable results for different values of dt, you must
      adapt std.
     	- As the noise generator provides a different current for each of its targets,
      the current recorded represents the instantaneous average of all the
      currents computed. When there exists only a single target, this would be
      equivalent to the actual current provided to that target.

Author:

    Ported to NEST2 API 08/2007 by Jochen Eppler, updated 07/2008 by HEP

SeeAlso:

- Device

Source:

    /opt/conda/conda-bld/nest_1510212701067/work/nest-2.14.0/models/noise_generator.h

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