R help - Apr 2012 - Error in gamma(delta + (complex(0, 0, 1) * (x - mu))/alpha) : unimplemented complex function

I am trying to obtain the grafic of a pdf . but this error keeps showing .
Here is the code 
MXN.fd = function(x,alpha,beta,mu,delta)
{
A = (2*cos(beta/2))^(2*delta)
B = 2*alpha*pi*gamma(2*delta)
C = (beta*(x-mu))/alpha
D = abs(gamma(delta + (complex(0,0,1)*(x-mu))/alpha)^2)
M = A/B*exp(C)*D
M
plot(x,M,type="l",lwd=2,col="red")

}

alpha = 0.02612297
beta = -0.50801886
mu = 0.00575829917
delta = 0.67395
x = x=seq(-0.04,0.04,length=200)

MXN.fd(x,alpha,beta,mu,delta)

i think the problem is the gamma function, does anyone know how to compute
gamma with imaginary numbers?

thanks in advance

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Guaramy <Guaramy <at> hotmail.com> writes:
> 
 [SNIP]
> i think the problem is the gamma function, does anyone know how to compute
> gamma with imaginary numbers?

  Try lngamma_complex() in the gsl package?

  Ben Bolker

> I am trying to obtain the grafic of a pdf . but this error keeps showing .
> Here is the code
Or use the complex gamma function gammaz() in package 'pracma'.
The following code works, that is produces a plot:

    library(pracma)
    MXN.fd <- function(x,alpha,beta,mu,delta) {
        A <- (2*cos(beta/2))^(2*delta)
        B <- 2*alpha*pi*gamma(2*delta)
        C <- (beta*(x-mu))/alpha
        D <- abs(gammaz(delta + (complex(0,0,1)*(x-mu))/alpha)^2)
        M <- A/B*exp(C)*D
        plot(x,M,type="l",lwd=2,col="red")
    }

    alpha <- 0.02612297; beta <- -0.50801886
    mu <- 0.00575829917; delta <- 0.67395
    x <- seq(-0.04,0.04,length=200)
    MXN.fd(x,alpha,beta,mu,delta)
    grid()
>
> i think the problem is the gamma function, does anyone know how to compute
> gamma with imaginary numbers?
>
> thanks in advance
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