# Command: testsuite::test_iaf_dc_aligned

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Name:

    testsuite::test_iaf_dc_aligned - sli script for test of iaf_neuron resolution independence

Synopsis:

    (test_iaf_dc_aligned) run -> compare response with reference data

Description:

      test_iaf_dc_aligned.sli is a modified version of test_iaf_dc. Here,
      we discuss and remove one of the problems of test_iaf_dc leading to
      simulation results not independent of the computation step size
      (resolution). The remaining flaw is corrected in the follow up script
      test_iaf_dc_delay.sli .

      The expected output is documented and briefly commented at the end of
      the script.

      The intention of this script is that the current starts to affect the
      neuron (is present from) at time t=3ms. By default, the delay of the
      connection between DC generator and neuron assumes the minimal value
      of 1 computation step h.  Therefore, the time stamp of the emitted
      current event needs to be 3ms	- h. according to the definitions of
      the timing scheme, the DC generator consequently needs to emit the
      appropriate event in the step 3ms	- 2h -> 3ms	- h.

      The property /start of a device specifies in ms the earliest time at
      which the device emits an event. This enables resolution independent
      specification of the emission time because at any computation step
      size h the device can be activated in the step start	- h ->
      start. The only requirement being that start	- h is a time larger or
      equal to the current time.  Otherwise the device cannot fulfill the
      request. The additional property /origin enables a shift of the
      device's time axis, see the documentation of devices for details. If
      resolution independence is desired origin should be specified in ms,
      often 0. is a useful value.  The above considerations result in the
      following settings for the DC generator device:

      /origin 0.	 % in ms
      /start arrival h sub   % in ms

      It should be pointed out that not specifying the delay of a
      connection in the .sli script, like it is done here

      dc_gen neuron Connect ;

      results in a simulation script that is not independent of the
      computation step size. This is because at the time of creation of the
      connection the minimal delay (1 computation step) is
      assumed. Therefore we have to compensate for this dependency in the
      start time of the DC generator as described above.  The alternative
      approach would be to specify a delay between the DC generator and the
      Neuron larger or equal to the largest computation time step to be
      used. This approach is investigated in

      test_iaf_dc_aligned.sli

Remarks:

      In earlier versions /start was defined to specify the time step t at
      which the device becomes activated, which is the transition t -> t+h.
      On the basis of this definition, the correct code was:

      /start  arrival 2 h mul sub	 % in ms

      During the development of this script a conversion problem of device
      start time expressed in ms was observed:

      dc_gen << /start  1.8  >> SetStatus
      dc_gen GetStatus /start get ==   --> 1.800000e+00
      dc_gen << /start  2.8  >> SetStatus
      dc_gen GetStatus /start get ==   --> 2.799000e+00

      For the purpose of this script, the problem was temporarily fixed by
      adding an epsilon 0.0001

      /start arrival 2 h mul sub 0.0001 add  % in ms

      The problem was fixed by Gewaltig 3.3.2004 and the code of this test
      script changed accordingly, Diesmann .

      Author:  February 2004, Diesmann, Gewaltig, Plesser

SeeAlso:

- testsuite::test_iaf_dc
- testsuite::test_iaf_dc_aligned_delay
- testsuite::test_iaf_dc_aligned_automatic

Source:

    /opt/conda/conda-bld/nest_1510212701067/work/nest-2.14.0/testsuite/unittests/test_iaf_dc_aligned.sli

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