Blow_opt: Blow internal parallel optimization function
In zanbi/DLMtool: Data-Limited Methods Toolkit

Find the current biomass at which it would take HZN mean generation times to reach Bfrac x SSBMSY biomass level given zero catches

Blow_opt(
  lnq,
  N,
  Asize_c,
  SSBMSYc,
  SSBpRc,
  MPA,
  SSB0c,
  nareas,
  retAc,
  MGThorizonc,
  Fc,
  Perrc,
  Mc,
  hc,
  Mac,
  Wac,
  R0c,
  Vc,
  nyears,
  maxage,
  movc,
  Spat_targc,
  SRrelc,
  aRc,
  bRc,
  Bfrac,
  maxF,
  mode = 1,
  plusgroup = 0
)

`lnq`	number: estimate of log catchability
`N`	marix maxage by nareas with initial numbers at age
`Asize_c`	vector length nareas with size of each area
`SSBMSYc`	number: spawning biomass at MSY
`SSBpRc`	vector length nareas with SSBpR by area
`MPA`	matrix of spatial closures
`SSB0c`	SSB0
`nareas`	numeric: number of areas
`retAc`	matrix maxage by nyears+proyears of retention by age and year
`MGThorizonc`	number: MGT x HZN
`Fc`	vector nyears long of fishing mortality rate
`Perrc`	vector nyears+maxage-1 long of recruitment devitions
`Mc`	matrix maxage by nyears+proyears of natural mortality rate
`hc`	number: steepness values
`Mac`	matrix nages by nyears+proyears of maturity at age
`Wac`	vector nages long of weight at age
`R0c`	number: unfished recruitment
`Vc`	matrix of vulnerability maxage x nyears
`nyears`	integer: number of historical years
`maxage`	integer: maximum age
`movc`	matrix of movement 2 x 2
`Spat_targc`	number: spatial targetting parameters
`SRrelc`	integer representing recruitmetn dynamics type 1: Bev Holt 2: Ricker
`aRc`	number: recruitment parameter
`bRc`	number: recruitment parameter
`Bfrac`	fraction of SSBMSY that is the target
`maxF`	maximum apical fishing mortality
`mode`	1: find Blow 2:report blow 3:plot results
`plusgroup`	Integer. Default = 0 = no plus-group. Use 1 to include a plus-group