NumberOfElectrons:

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   Computes the number of electrons.

   Typing NumberOfElectrons gives the electrons in a D-T reaction.

   Type NumberOfElectrons for a demo.
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   Form:
   nE = NumberOfElectrons( nI, zI )
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   Inputs
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   nI        (1,2)  Number densities of the constituents
   zI        (1,2)  Atomic numbers

   -------
   Outputs
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   nE         (1,1) Number of electrons   

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