GNU Scientific Library – Reference Manual: Trigamma Function

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#### 7.28.2 Trigamma Function

Function: double gsl_sf_psi_1_int (int n)
Function: int gsl_sf_psi_1_int_e (int n, gsl_sf_result * result)

  These routines compute the Trigamma function \psi'(n) for positive integer n.

Function: double gsl_sf_psi_1 (double x)
Function: int gsl_sf_psi_1_e (double x, gsl_sf_result * result)

  These routines compute the Trigamma function \psi'(x) for general x.