@brief Function that calculates the value of the Gamma distribution @f$f_\Gamma(x,\kappa,\theta) =
\frac{1}{\Gamma(\kappa) \theta^\kappa}x^{\kappa-1}\exp{\left(-x/\theta\right)}@f$.
@param x Variable @f$x@f$ of @f$f_\Gamma(x,\kappa,\theta)@f$.
@param k Shape factor @f$\kappa@f$ of @f$f_\Gamma(x,\kappa,\theta)@f$.
@param t Scale factor @f$\theta@f$ of @f$f_\Gamma(x,\kappa,\theta)@f$.
@param fGamma Computed value of @f$f_\Gamma(x,\kappa,\theta)@f$.
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FUNCTION fGamma(x,k,t)REAL(rp),INTENT(IN)::xREAL(rp),INTENT(IN)::kREAL(rp),INTENT(IN)::tREAL(rp)::fGammafGamma=x**(k-1.0_rp)*EXP(-x/t)/(GAMMA(k)*t**k)END FUNCTION fGamma