text: #ifndef STAN_MATH_PRIM_SCAL_FUN_MODIFIED_BESSEL_FIRST_KIND_HPP
  #define STAN_MATH_PRIM_SCAL_FUN_MODIFIED_BESSEL_FIRST_KIND_HPP
  
  #include <stan/math/prim/meta.hpp>
  #include <boost/math/special_functions/bessel.hpp>
  #include <stan/math/prim/scal/err/check_not_nan.hpp>
  
  namespace stan {
  namespace math {
  
  /**
   *
     \f[
     \mbox{modified\_bessel\_first\_kind}(v, z) =
     \begin{cases}
       I_v(z) & \mbox{if } -\infty\leq z \leq \infty \\[6pt]
       \textrm{error} & \mbox{if } z = \textrm{NaN}
     \end{cases}
     \f]
  
     \f[
     \frac{\partial\, \mbox{modified\_bessel\_first\_kind}(v, z)}{\partial z} =
     \begin{cases}
       \frac{\partial\, I_v(z)}{\partial z} & \mbox{if } -\infty\leq z\leq \infty
   \\[6pt] \textrm{error} & \mbox{if } z = \textrm{NaN} \end{cases} \f]
  
     \f[
       {I_v}(z) = \left(\frac{1}{2}z\right)^v\sum_{k=0}^\infty
   \frac{\left(\frac{1}{4}z^2\right)^k}{k!\Gamma(v+k+1)} \f]
  
       \f[
       \frac{\partial \, I_v(z)}{\partial z} = I_{v-1}(z)-\frac{v}{z}I_v(z)
       \f]
   *
   */
  template <typename T2>
  inline T2 modified_bessel_first_kind(int v, const T2 z) {
    check_not_nan("modified_bessel_first_kind", "z", z);
  
    return boost::math::cyl_bessel_i(v, z);
  }
  
  }  // namespace math
  }  // namespace stan
  
  #endif
  