title: DEoptim package - Argument is missing with no default
body: <p>Im trying to use DEoptim to find the global minimum of z in in -1 &lt; x &lt; 1 , -1 &lt; y &lt; 1, but im getting <code>Error in FUN(newX[, i], ...) : argument "y" is missing, with no default</code> and I dont know what im supposed to do for the mission "y"</p>
  
  <pre><code>install.packages("Rmpfr")
  install.packages("DEoptim")
  library(gmp)
  library(Rmpfr)
  library(parallel) # https://cran.r-project.org/web/packages/DEoptim/vignettes/DEoptim.pdf
  library(DEoptim)
  
  z = function(x,y) {
    (exp(sin(60.0*x)) + sin(50.0*exp(y)) + sin(80.0*sin(x)) + sin(sin(70.0*y)) - sin(10.0*(x+y)) + (x*x+y*y)/4.0)
  }
  
  optimized_Minimum &lt;- DEoptim(z, lower = c(-1,-1), upper = c(1,1),
                               control=list(storepopfrom=1, trace=FALSE))
  # optimized_Minimum &lt;- optim(z, lower = c(-1,-1), upper = c(1,1), method = "Brent")
  </code></pre>