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Nexxim Simulator >
Nexxim Harmonic Balance >
   Harmonic Balance Technical Notes >
       Controlling Nexxim Harmonic Balance Analysis >
           Initial Guess for Vector of Node Voltages               


Initial Guess for Vector of Node Voltages

The option initial_guess can be used to control the initial guess for the vectors of node voltages and currents used in the harmonic balance calculation.

Fewer Tones Initial Guess

initial_guess=fewer_tones is the default for multi-tone analysis. For single-tone analysis, fewer_tones has the same effect as initial_guess=dc (performs a DC analysis, then starts harmonic balance with the DC values as the initial guess). For multitone analyses, fewer_tones starts with the DC operating point as the initial guess and solves the circuit with only the first tone enabled. The values with the 1-tone analysis are used as the initial guess for the analysis of the circuit with the first two tones enabled, and so on until the circuit has been solved with all tones enabled. For example, if the netlist contains:

.OPTIONS hb.initial_guess=fewer_tones

.HB tones=(1e6, 1.1e7, 2.1e7) maxk=(3,4,5)

The simulator first calculates the DC operating point, then uses those values as the initial guess in solving the single-tone analysis using tone 1e6Hz. The values from the 1-tone analysis then become the initial guess for the two-tone analysis using tones 1e6Hz and 1.1e7Hz. The result from the two-tone analysis then become the initial guess for the full analysis using all three tones.

Fewer Tones Transient Initial Guess

initial_guess=fewer_tones_transient solves the 1-tone problem using transient analysis, then proceeds to solve the multitone problems with the fewer_tones algorithm described above. This option has two subordinate options.

•  initial_guess.fewer_tones_transient.tmax=val sets the maximum step size. There is no default.

•  initial_guess.fewer_tones_transient.tstop=val specifies the stop time.

DC Initial Guess

initial_guess=dc performs a DC analysis, then starts harmonic balance with the DC values as the initial guess. DC is the default for single-tone analysis.

Zero Initial Guess

initial_guess=zero starts harmonic balance with vectors of zero voltages and currents as the initial guess.

File Initial Guess

initial_guess=file uses vectors of node voltages and currents saved from a previous harmonic balance simulation. When file is the source for the initial guess, the netlist option statement must also include an initial_guess_file=[pathname]filename option to identify the file. The filename specifies the name of an SDF-format file generated by a previous run of HB. The pathname can be omitted if the file is in the directory where the netlist resides. The pathname can specify a subdirectory in the current directory; otherwise, the pathname must provide the full directory path. See External Files in the Netlist File Format help topic for details.

 

Note 

The pathname and filename of the initial guess file from a previous run of HB must not be the same as the pathname and filename of the output file to be generated by the current run of HB. That is, HB cannot read old values from and write new values to the same file.

Transient Initial Guess

initial_guess=transient performs a transient analysis, then uses the final values as the initial guess for the harmonic balance analysis. When transient is the source for the initial guess, the netlist option statement can also include two additional options to control the transient analysis.

•  initial_guess.transient.tmax=val suggests a maximum step size to use.

•  initial_guess.transient.tstop=val sets the stop time.

Initial Guess in Sweeps

By default, harmonic balance applies the initial guess strategy at the beginning of each iteration of a sweep. A separate option, result_as_initial_guess, controls this behavior.

•  result_as_initial_guess=0 turns off the use of previous results.

•  result_as_initial_guess=1 enables the use of previous results. However, the use of previous results is the default, so this option setting is never needed.




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