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roptimizationconstraintsuniroot
user1375871
user1375871

Reputation: 1259

nsga2 Constraints - mco package in R

My objective function considers ellipse arc lengths. Within the objective function, I use uniroot to find the semi-minor axis b for the semi-major a and arc angle provided by nsga.

I've written a constraint function to ensure that the limits provided to uniroot are of opposite sign.... but it's not working. The program crashes becasue f() values are not of opposite sign.

I've simplified the program to the example below... was hoping for help on getting this to work. Thank you.

library(RConics)
library(mco)


###############################################################
#FUNCTIONS
###############################################################

restricts<-function(invec,len){
  lwr<-sign(get_b(1, as.numeric(invec[1]), len, as.numeric(invec[2]))) 
  uppr<-sign(get_b(as.numeric(invec[1]), as.numeric(invec[1]), len, as.numeric(invec[2])))
  
  restrictions <- logical(1)
  restrictions[1] <- (lwr != uppr)
  return (restrictions)
  
}


objective<-function(invec, len){
  a<-as.numeric(invec[1])
  theta=as.numeric(invec[2])
  
  b_out<-uniroot(get_b,c(1,a),a=a,len=len,theta=theta)
  b<-b_out$root
  
  ps<- c(
    a*cos(d2r(90+theta)), 
    b*sin(d2r(90+theta))
  )
  
  end<-   atan(-b*cot(d2r(180+(90-theta)))/a) - pi/2+pi/2
  rot <- 0.52-end
  
  final<- RotMat(rot)%*%ps
  
  return(abs(final[2]))
}

r2d<-function(theta) theta*180/pi
d2r<-function(theta) theta*pi/180
RotMat<-function(theta) rbind(c(cos(theta),-sin(theta)),c(sin(theta),cos(theta)))

get_b<-function(b,a,len,theta){
  return(
    len-arcLengthEllipse(
      p1 = c(0,b), 
      p2 = c(a*cos(d2r(90+theta)), b*sin(d2r(90+theta))), 
      saxes = c(a,b), 
      n = 5)
  )
}




###############################################################
#MAIN
###############################################################

mods<-nsga2(objective, idim=2, odim=1, 
            constraints = restricts,
            cdim=1,
            generations=10, popsize=100,
            cprob=0.9, cdist=1,
            mprob=0.2, mdist=20,
            lower.bounds = c(130,1), #70.6, 86.6
            upper.bounds = c(203,90),
            len=204)

Upvotes: 2

Views: 292

Answers (0)

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