1
我想優化(最大)以下函數f1
。我寫了下面的代碼,它使用下限和上限,因爲我們知道所有參數都等於或大於零,並且我們總是應該有x4
值小於或等於x6
。我如何解決R中的這個問題?我想獲得函數的有限最大值f1
。R中函數的優化(L-BFGS-B需要有限的'fn')
x1 = 0.1
x2 = 0.1
x3 = 2
x4 = 10
x5 = 2
x6 = 30
x7 = 1
par = list(x1=x1, x2=x2, x3=x3, x4=x4,x5=x5, x6=x6, x7=x7)
par1 = c(1, 1, 2, 1.5, 1, 1.5, 1)
f1 = function(x, par){
sum(log(exp(-(par$x7)*(par$x1*x + par$x2*x^2/2 +
par$x3 * (par$x4-x)^3/3+par$x5 *(x-par$x6)^3/3))))
}
x = seq(0, 500, length=100)
z = c(par$x1, par$x2, par$x3, par$x4, par$x5, par$x6, par$x7)
f2 = function(z){
par.new = list(x1 = z[1], x2 = z[2], x3 = z[3], x4 = z[4]
, x5 = z[5], x6 = z[6], x7 = z[7])
f1(x, par.new)
}
optim(par1, f2, method = "L-BFGS-B", lower = rep(0, length(z)),
upper = rep(Inf,length(z)),control = list(trace = 5,fnscale=-1))
> optim(par1, f2, method = "L-BFGS-B", lower = rep(0, length(z)),
upper = rep(Inf, length(z)), control = list(trace = 5,fnscale=-1))
N = 7, M = 5 machine precision = 2.22045e-16
L = 0 0 0 0 0 0 0
X0 = 1 1 2 1.5 1 1.5 1
U = inf inf inf inf inf inf inf
At X0, 0 variables are exactly at the bounds
Error in optim(par1, f2, method = "L-BFGS-B", lower = rep(0, length(z)), :
L-BFGS-B needs finite values of 'fn'
'f1(x,par)'取決於參數矢量,也取決於變量'x'。那麼你是否試圖找到爲給定的一組參數而最大化'f1'的'x'的值,或者你是否想要爲給定的'x'找到最大化'f1'的一組參數?或者是別的什麼?? – jlhoward
@jilhoward。我試圖找到一組參數,使給定的x最大化f1。 – rose