Hello again.
Thank you for the comments. I have written these codes.

iy=function(x)
{
res=NULL
ress=0
for (i in (1:2))
{
for (xx in x[i])
{
fy=function(y) (exp(-exp(y+log(xx)))*(-exp(y+log(xx)))^2)/(1-exp(-exp(y+log(xx))))
res=c(res,integrate(fy,-6.907,-1.246)$value)
ress=ress+res
}
}
return(ress)
}
iy(c(1,1))
integrate(fy,-6.907,-1.246)$value

In 1D optimize() works perfectly on iy(). However the problem is in 2D and more, optimize() does not work and I need to apply optim(). I could not apply optim() on iy().

Beside, I tried to use Ryacas, I faced with this error:
[1] "Starting Yacas!"
Error in socketConnection(host = "127.0.0.1", port = 9734, server = FALSE, :
cannot open the connection
In addition: Warning message:
In socketConnection(host = "127.0.0.1", port = 9734, server = FALSE, :
127.0.0.1:9734 cannot be opened

Cheers,
Maryam

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