rm(list=ls())
require(animation)
require(fields)

grid.l<-list( abcissa= seq(0,15,,16), ordinate= seq(0,15,,16)) 
xg<-make.surface.grid( grid.l)

## set animation options
oopt <- ani.options(interval = 0.6)

numSteps<-50
xy1<-c(5,7)
xy2<-c(4,8)
uv<-xy2-xy1
plot(xg,pch='o',cex=0.3)
xyFood<-c(12,12)
J<-rep(0,numSteps)
Theta<-runif(7)

for (time in seq(1,numSteps)){
  
  if (uv[1]==1 && uv[2]==1){
    
    if(runif(1)<Theta[1]){
      uv[1]<-0
    }else{
      uv[2]<-0
    }
    
  }else if (uv[1]==0 && uv[2]==1){
    
    if(runif(1)<Theta[2]){
      uv[1]<-1
    }else{
      uv[1]<-(-1)
    }
    
  }else if (uv[1]==(-1) && uv[2]==1){
    
    if(runif(1)<Theta[3]){
      uv[1]<-0
    }else{
      uv[2]<-(0)
    }
    
  }else if (uv[1]==(-1) && uv[2]==0){
    
    if(runif(1)<Theta[4]){
      uv[2]<-1
    }else{
      uv[2]<-(-1)
    }
    
  }else if (uv[1]==(-1) && uv[2]==(-1)){
    
    if(runif(1)<Theta[5]){
      uv[1]<-0
    }else{
      uv[2]<-0
    }
    
  }else if (uv[1]==0 && uv[2]==(-1)){
    
    if(runif(1)<0.5){
      uv[1]<-(-1)
    }else{
      uv[1]<-(1)
    }
    
  }else if (uv[1]==1 && uv[2]==(-1)){
    
    if(runif(1)<Theta[6]){
      uv[1]<-0
    }else{
      uv[2]<-0
    }
    
  }else if (uv[1]==1 && uv[2]==0){
    
    if(runif(1)<Theta[7]){
      uv[2]<-1
    }else{
      uv[2]<-(-1)
    }
    
  }
  
  if (runif(1)<0.5){
    xy2<-(xy1+uv)
  }else{
    xy1<-(xy2-uv)
  }
  
  plot(xg,pch='o',cex=0.3)
  points(xyFood[1],xyFood[2],pch=15,cex=1,col='green')
  lines(c(xy1[1],xy2[1]),c(xy1[2],xy2[2]))
  ani.pause()
  par(new=FALSE)
  J[time]<-(1/2)*(sqrt(((xyFood[1]-xy1[1])^2)+((xyFood[2]-xy1[2])^2))+sqrt(((xyFood[1]-xy2[1])^2)+((xyFood[2]-xy2[2])^2)))  

}

plot(J,type='l',col='blue',xlab="Step Number",ylab="Distance to Food")
grid()