Clarification regarding Frequency Analysis

Hi All,
 
I was seeking a clarification regarding the behavior of a VHDL-AMS
simultaneous statement during frequency analysis. Any help is greatly
appreciated.
 
Consider the following source model - this model is similar to the one
in the "The System Designer's Guide to VHDL-AMS" by Peter Ashenden (pp
407).
 
LIBRARY IEEE;
USE IEEE.MATH_REAL.MATH_2_PI;
USE IEEE.ELECTRICAL_SYSTEMS.ALL;

ENTITY E IS
    PORT (QUANTITY DC : IN VOLTAGE := 1.0;
          QUANTITY AC_MAG : IN VOLTAGE := 1.0;
          QUANTITY AC_PHASE : IN ANGLE := 0.0;
          TERMINAL p,m: ELECTRICAL);
END ENTITY E;
ARCHITECTURE behav OF E IS
    QUANTITY v ACROSS i THROUGH p TO m;
    QUANTITY ac_spec : real SPECTRUM AC_MAG, MATH_2_PI*AC_PHASE/360.0;
BEGIN
    IF (domain = quiescent_domain) OR (domain = time_domain) USE
       v == DC;
    ELSE
      v == ac_spec;
    END USE;
END ARCHITECTURE behav;
 
My question is - Why is the if-use required at all? Wouldn't the same
effect be achieved by using the following simultaneous statement -
 
v == DC + ac_spec;
 
i.e. Does the quantity DC have any contribution in the frequency domain?
 
Thanks,
Sameer

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