Dear R users,
i try to integrate lgamma from 0 to Inf. But here i get the message "roundoff
error is detected in the extrapolation table", if i use 1.0e120 instead of Inf
the computation works, but this is against the suggestion of integrates help
information to use Inf explicitly. Using stirlings approximation doesnt bring
the solution too.
## Stirlings approximation
lgammaApprox <- function(x)
{
0.5*log(2*pi)+(x-(1/2))*log(x)-x
}
integrate(lgamma, lower = 0, upper = 1.0e120)
integrate(lgammaApprox, lower = 0, upper = 1.0e120)
> integrate(lgamma, lower = 0, upper = 1.0e120)
1.374051e+242 with absolute error < 3.2e+235
> integrate(lgammaApprox, lower = 0, upper = 1.0e120)
1.374051e+242 with absolute error < 3.2e+235
integrate(lgamma, lower = 0, upper = Inf)
integrate(lgammaApprox, lower = 0, upper = Inf)
> integrate(lgamma, lower = 0, upper = Inf)
Fehler in integrate(lgamma, lower = 0, upper = Inf) :
roundoff error is detected in the extrapolation table
> integrate(lgammaApprox, lower = 0, upper = Inf)
Fehler in integrate(lgammaApprox, lower = 0, upper = Inf) :
roundoff error is detected in the extrapolation table
Many thanks if you have any advice for me!
best regards
Andreas
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