Re: [R] Problem with minimization that I failed to understand

Rui Barradas Thu, 27 Mar 2025 12:29:09 -0700

Às 18:35 de 27/03/2025, Daniel Lobo escreveu:

Hi,


I have below minimization problem


MyDat = structure(list(c(50L, 0L, 0L, 50L, 75L, 100L, 50L, 0L, 50L, 0L,
25L, 50L, 50L, 75L, 75L, 75L, 0L, 75L, 75L, 75L, 0L, 25L, 75L,
75L, 0L, 75L, 100L, 0L, 25L, 100L), c(75L, 0L, 0L, 50L, 100L,
50L, 75L, 75L, 100L, 25L, 0L, 25L, 100L, 0L, 50L, 0L, 25L, 25L,
100L, 75L, 0L, 0L, 0L, 50L, 0L, 75L, 75L, 0L, 50L, 25L), c(50L,
0L, 0L, 0L, 100L, 25L, 0L, 0L, 25L, 50L, 0L, 25L, 75L, 50L, 100L,
50L, 0L, 75L, 25L, 50L, 0L, 0L, 25L, 0L, 50L, 100L, 100L, 0L,
75L, 50L), c(25L, 0L, 0L, 75L, 75L, 25L, 50L, 50L, 100L, 25L,
0L, 100L, 50L, 25L, 100L, 25L, 25L, 100L, 50L, 100L, 0L, 0L,
100L, 50L, 0L, 50L, 75L, 0L, 50L, 25L), c(50L, 0L, 0L, 75L, 75L,
75L, 25L, 25L, 0L, 100L, 0L, 25L, 25L, 75L, 100L, 0L, 25L, 0L,
75L, 25L, 25L, 25L, 75L, 25L, 0L, 75L, 100L, 0L, 100L, 100L),
     c(50L, 0L, 0L, 50L, 100L, 25L, 25L, 25L, 50L, 50L, 0L, 50L,
     75L, 0L, 100L, 50L, 25L, 100L, 50L, 75L, 0L, 0L, 50L, 25L,
     0L, 100L, 100L, 0L, 75L, 50L), c(50L, 0L, 0L, 50L, 75L, 25L,
     75L, 50L, 100L, 25L, 0L, 75L, 25L, 0L, 50L, 0L, 50L, 75L,
     100L, 75L, 0L, 0L, 100L, 0L, 0L, 50L, 75L, 0L, 100L, 100L
     ), c(25L, 75L, 50L, 25L, 75L, 50L, 100L, 75L, 100L, 25L,
     0L, 75L, 25L, 50L, 25L, 25L, 75L, 75L, 100L, 75L, 75L, 100L,
     75L, 25L, 0L, 75L, 75L, 0L, 75L, 100L), c(55L, 30L, 20L,
     30L, 45L, 30L, 30L, 30L, 70L, 30L, 10L, 45L, 45L, 45L, 45L,
     30L, 30L, 55L, 45L, 45L, 30L, 30L, 30L, NA, 30L, 55L, 45L,
     20L, 45L, 70L), c(85L, 40L, 40L, 40L, 55L, 40L, 20L, 30L,
     30L, 30L, 20L, 30L, 70L, 40L, 85L, 55L, 30L, 40L, 30L, 55L,
     20L, 30L, 55L, 0L, 40L, 55L, 70L, 40L, 85L, 70L), c(45L,
     45L, 0L, 45L, 45L, 45L, 0L, 0L, 100L, 45L, 0L, 100L, 45L,
     45L, 100L, 45L, 45L, 100L, 45L, 45L, 45L, 45L, 25L, 45L,
     0L, 100L, 45L, 0L, 45L, 45L), c(55L, 45L, 45L, 45L, 55L,
     45L, 45L, 45L, 45L, 45L, 45L, 45L, 45L, 45L, 55L, 55L, 45L,
     55L, 45L, 45L, 45L, 45L, 45L, 45L, 45L, 55L, 45L, 45L, 45L,
     45L), c(100L, 100L, 50L, 100L, 100L, 100L, 100L, 100L, 100L,
     100L, 50L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L,
     100L, 100L, 100L, 100L, 50L, 100L, 100L, 100L, 100L, 100L,
     100L), c(100L, 25L, 25L, 0L, 100L, 60L, 0L, 0L, 25L, 60L,
     0L, 60L, 100L, 60L, 100L, 100L, 25L, 100L, 60L, 100L, 100L,
     60L, 100L, 60L, 100L, 100L, 100L, 100L, 60L, 60L), c(0L,
     0L, 50L, 50L, 100L, 100L, 0L, 0L, 100L, 100L, 0L, 100L, 100L,
     0L, 100L, 100L, 0L, 100L, 100L, 100L, 100L, 100L, 100L, 0L,
     100L, 100L, 100L, 100L, 100L, 100L), c(40L, 100L, 40L, 100L,
     100L, 40L, 100L, 100L, 100L, 40L, 100L, 100L, 100L, 100L,
     100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L,
     100L, 100L, 100L, 0L, 100L, 100L), c(100L, 100L, 100L, 100L,
     100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L,
     100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, -10L,
     100L, 100L, 100L, -10L, 100L, 100L), c(70L, 0L, 25L, 0L,
     100L, 25L, 0L, 0L, 0L, 45L, 0L, 25L, 100L, 100L, 100L, 100L,
     0L, 70L, 0L, 100L, 45L, 45L, 0L, 0L, 100L, 100L, 100L, 0L,
     100L, 100L), c(55L, 55L, 55L, 55L, 55L, 55L, 55L, 55L, 55L,
     55L, 55L, 55L, 55L, 55L, 55L, 55L, 20L, 55L, 20L, 55L, 20L,
     20L, 100L, 55L, 55L, 55L, 55L, 0L, 55L, 55L), c(65L, 65L,
     100L, 65L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L,
     100L, 100L, 100L, 100L, 65L, 100L, 100L, 100L, 65L, 100L,
     0L, 65L, 100L, 100L, 100L, 100L, 100L, 100L), c(85L, 85L,
     85L, 85L, 85L, 85L, 85L, 85L, 85L, 85L, 85L, 85L, 56L, 85L,
     100L, 85L, 85L, 85L, 0L, 85L, 85L, 85L, 85L, 85L, 85L, 85L,
     85L, 28L, 56L, 56L)), row.names = c(NA, -30L), class = "data.frame")

Fn = function(Wts) return(-Kendall::Kendall(1:Nobs,
rank(-as.vector(as.matrix(MyDat) %*% matrix(Wts, nc = 1)[, 1, drop =
T])))$tau[1])
q1 = pracma::fmincon(c(0.12, 0.04, 0.07, 0.03, 0.06, 0.07, 0.07, 0.04,
0.09, 0.08, 0.02, 0.02, 0.03, 0.06, 0.02, 0, 0.07, 0.05, 0.02, 0.02, 0.02),
fn = Fn,
           A = matrix(c(rep(0, 20), -1), nrow = 1), b = -2.05/100, Aeq =
matrix(c(rep(1, 20), 1), nrow = 1), beq = 1,
           lb = rep(0.01, 21),
           tol = 1e-16, maxfeval = 10000000, maxiter = 5000000)


However with above code, I got sub-optimal value in terms of minimization
of the objective function:

q1$value
#0.1632184
Fn(c(0.12, 0.04, 0.07, 0.03, 0.06, 0.07, 0.07, 0.04, 0.09, 0.08, 0.02,
0.02, 0.03, 0.06, 0.02, 0, 0.07, 0.05, 0.02, 0.02, 0.02))
#0.1586207

Could you please help me to understand what went wrong with my code and how
to correct that?

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Hello,

I cannot reproduce your result.
Instead of checking the result with


Fn(c(0.12, 0.04, 0.07, etc, ...)

pass the actual return value, q1$par. That's what I did and the resultmatches the function minimum.

Here is the code I ran.




MyDat <- structure(list(
  c(50L, 0L, 0L, 50L, 75L, 100L, 50L, 0L, 50L, 0L,
    25L, 50L, 50L, 75L, 75L, 75L, 0L, 75L, 75L, 75L, 0L, 25L, 75L,
    75L, 0L, 75L, 100L, 0L, 25L, 100L),
  c(75L, 0L, 0L, 50L, 100L,
    50L, 75L, 75L, 100L, 25L, 0L, 25L, 100L, 0L, 50L, 0L, 25L, 25L,
    100L, 75L, 0L, 0L, 0L, 50L, 0L, 75L, 75L, 0L, 50L, 25L),
  c(50L, 0L, 0L, 0L, 100L, 25L, 0L, 0L, 25L, 50L, 0L, 25L, 75L, 50L, 100L,
    50L, 0L, 75L, 25L, 50L, 0L, 0L, 25L, 0L, 50L, 100L, 100L, 0L,
    75L, 50L),
  c(25L, 0L, 0L, 75L, 75L, 25L, 50L, 50L, 100L, 25L,
    0L, 100L, 50L, 25L, 100L, 25L, 25L, 100L, 50L, 100L, 0L, 0L,
    100L, 50L, 0L, 50L, 75L, 0L, 50L, 25L),
  c(50L, 0L, 0L, 75L, 75L,
    75L, 25L, 25L, 0L, 100L, 0L, 25L, 25L, 75L, 100L, 0L, 25L, 0L,
    75L, 25L, 25L, 25L, 75L, 25L, 0L, 75L, 100L, 0L, 100L, 100L),
  c(50L, 0L, 0L, 50L, 100L, 25L, 25L, 25L, 50L, 50L, 0L, 50L,
    75L, 0L, 100L, 50L, 25L, 100L, 50L, 75L, 0L, 0L, 50L, 25L,
    0L, 100L, 100L, 0L, 75L, 50L),
  c(50L, 0L, 0L, 50L, 75L, 25L,
    75L, 50L, 100L, 25L, 0L, 75L, 25L, 0L, 50L, 0L, 50L, 75L,
    100L, 75L, 0L, 0L, 100L, 0L, 0L, 50L, 75L, 0L, 100L, 100L),
  c(25L, 75L, 50L, 25L, 75L, 50L, 100L, 75L, 100L, 25L,
    0L, 75L, 25L, 50L, 25L, 25L, 75L, 75L, 100L, 75L, 75L, 100L,
    75L, 25L, 0L, 75L, 75L, 0L, 75L, 100L),
  c(55L, 30L, 20L,
    30L, 45L, 30L, 30L, 30L, 70L, 30L, 10L, 45L, 45L, 45L, 45L,
    30L, 30L, 55L, 45L, 45L, 30L, 30L, 30L, NA, 30L, 55L, 45L,
    20L, 45L, 70L),
  c(85L, 40L, 40L, 40L, 55L, 40L, 20L, 30L,
    30L, 30L, 20L, 30L, 70L, 40L, 85L, 55L, 30L, 40L, 30L, 55L,
    20L, 30L, 55L, 0L, 40L, 55L, 70L, 40L, 85L, 70L),
  c(45L, 45L, 0L, 45L, 45L, 45L, 0L, 0L, 100L, 45L, 0L, 100L, 45L,
    45L, 100L, 45L, 45L, 100L, 45L, 45L, 45L, 45L, 25L, 45L,
    0L, 100L, 45L, 0L, 45L, 45L),
  c(55L, 45L, 45L, 45L, 55L,
    45L, 45L, 45L, 45L, 45L, 45L, 45L, 45L, 45L, 55L, 55L, 45L,
    55L, 45L, 45L, 45L, 45L, 45L, 45L, 45L, 55L, 45L, 45L, 45L, 45L),
  c(100L, 100L, 50L, 100L, 100L, 100L, 100L, 100L, 100L,
    100L, 50L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L,
    100L, 100L, 100L, 100L, 50L, 100L, 100L, 100L, 100L, 100L, 100L),
  c(100L, 25L, 25L, 0L, 100L, 60L, 0L, 0L, 25L, 60L,
    0L, 60L, 100L, 60L, 100L, 100L, 25L, 100L, 60L, 100L, 100L,
    60L, 100L, 60L, 100L, 100L, 100L, 100L, 60L, 60L),
  c(0L, 0L, 50L, 50L, 100L, 100L, 0L, 0L, 100L, 100L, 0L, 100L, 100L,
    0L, 100L, 100L, 0L, 100L, 100L, 100L, 100L, 100L, 100L, 0L,
    100L, 100L, 100L, 100L, 100L, 100L),
  c(40L, 100L, 40L, 100L,
    100L, 40L, 100L, 100L, 100L, 40L, 100L, 100L, 100L, 100L,
    100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L,
    100L, 100L, 100L, 0L, 100L, 100L),
  c(100L, 100L, 100L, 100L,
    100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L,
    100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, -10L,
    100L, 100L, 100L, -10L, 100L, 100L),
  c(70L, 0L, 25L, 0L,
    100L, 25L, 0L, 0L, 0L, 45L, 0L, 25L, 100L, 100L, 100L, 100L,
    0L, 70L, 0L, 100L, 45L, 45L, 0L, 0L, 100L, 100L, 100L, 0L,
    100L, 100L),
  c(55L, 55L, 55L, 55L, 55L, 55L, 55L, 55L, 55L,
    55L, 55L, 55L, 55L, 55L, 55L, 55L, 20L, 55L, 20L, 55L, 20L,
    20L, 100L, 55L, 55L, 55L, 55L, 0L, 55L, 55L),
  c(65L, 65L,
    100L, 65L, 100L, 100L, 100L, 100L, 100L, 100L, 100L, 100L,
    100L, 100L, 100L, 100L, 65L, 100L, 100L, 100L, 65L, 100L,
    0L, 65L, 100L, 100L, 100L, 100L, 100L, 100L),
  c(85L, 85L,
    85L, 85L, 85L, 85L, 85L, 85L, 85L, 85L, 85L, 85L, 56L, 85L,
    100L, 85L, 85L, 85L, 0L, 85L, 85L, 85L, 85L, 85L, 85L, 85L,
    85L, 28L, 56L, 56L)),
  row.names = c(NA, -30L), class = "data.frame")



Fn <- function(Wts) return(
  Kendall::Kendall(
    1:Nobs,

rank(-as.vector(as.matrix(MyDat) %*% matrix(Wts, nc = 1)[, 1, drop= T]))

  )$tau[1]
)

Nobs <- nrow(MyDat)

q1 <- pracma::fmincon(
  c(0.12, 0.04, 0.07, 0.03, 0.06, 0.07, 0.07, 0.04, 0.09, 0.08,
    0.02, 0.02, 0.03, 0.06, 0.02, 0, 0.07, 0.05, 0.02, 0.02, 0.02),
  fn = Fn,
  A = matrix(c(rep(0, 20), -1), nrow = 1), b = -2.05/100,
  Aeq = matrix(c(rep(1, 20), 1), nrow = 1), beq = 1,
  lb = rep(0.01, 21),
  tol = 1e-16,
  maxfeval = 10000000,
  maxiter = 5000000
)

q1$value
#> [1] -0.1632184
Fn(q1$par)
#> [1] -0.1632184



Hope this helps,

Rui Barradas


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______________________________________________
[email protected] mailing list -- To UNSUBSCRIBE and more, see
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PLEASE do read the posting guide https://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Re: [R] Problem with minimization that I failed to understand

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