txt: ## dist_zef-FRITH-Math-Libgsl-Function.md
  ## Chunk 3 of 3
  ) is export(:lambert)
  
  These compute the principal branch of the Lambert W function, W₀(x).
  
  ### sub lambert-Wm1(Num(Cool) $x --> Num) is export(:lambert)
  
  ### sub lambert-Wm1-e(Num(Cool) $x --> List) is export(:lambert)
  
  These compute the principal branch of the Lambert W function, W₋₁(x).
  
  ### sub legendre-P1(Num(Cool) $x --> Num) is export(:legendre)
  
  ### sub legendre-P1-e(Num(Cool) $x --> List) is export(:legendre)
  
  ### sub legendre-P2(Num(Cool) $x --> Num) is export(:legendre)
  
  ### sub legendre-P2-e(Num(Cool) $x --> List) is export(:legendre)
  
  ### sub legendre-P3(Num(Cool) $x --> Num) is export(:legendre)
  
  ### sub legendre-P3-e(Num(Cool) $x --> List) is export(:legendre)
  
  These functions evaluate the Legendre polynomials Pₗ(x) using explicit representations for l = 1, 2, 3.
  
  ### sub legendre-Pl(UInt $l, Num(Cool) $x where -1 ≤ \* ≤ 1 --> Num) is export(:legendre)
  
  ### sub legendre-Pl-e(UInt $l, Num(Cool) $x where -1 ≤ \* ≤ 1 --> List) is export(:legendre)
  
  These functions evaluate the Legendre polynomial Pₗ(x) for a specific value of l, x.
  
  ### sub legendre-Pl-array(UInt $lmax, Num(Cool) $x where -1 ≤ \* ≤ 1 --> List) is export(:legendre)
  
  ### sub legendre-Pl-deriv-array(UInt $lmax, Num(Cool) $x where -1 ≤ \* ≤ 1 --> List) is export(:legendre)
  
  These functions compute arrays of Legendre polynomials Pₗ(x) and derivatives dPₗ(x)/dx for l = 0 … lmax.
  
  ### sub legendre-Q0(Num(Cool) $x where
  
  ### sub legendre-Q0-e(Num(Cool) $x where
  
  These routines compute the Legendre function Q₀(x).
  
  ### sub legendre-Q1(Num(Cool) $x where
  
  ### sub legendre-Q1-e(Num(Cool) $x where
  
  These routines compute the Legendre function Q₁(x).
  
  ### sub legendre-Ql(UInt $l, Num(Cool) $x where { $\_ > -1 && $\_ ≠ 1 } --> Num) is export(:legendre)
  
  ### sub legendre-Ql-e(UInt $l, Num(Cool) $x where { $\_ > -1 && $\_ ≠ 1 } --> List) is export(:legendre)
  
  These routines compute the Legendre function Qₗ(x).
  
  ### sub legendre-array-index(UInt $l, UInt $n --> UInt) is export(:legendre)
  
  This function returns the index into the result array, corresponding to Pⁿₗ(x), P’ⁿₗ, or P”ⁿₗ(x).
  
  ### sub legendre-array(Int $norm, size\_t $lmax where \* ≤ 150, Num(Cool) $x where -1 ≤ \* ≤ 1 --> List) is export(:legendre)
  
  ### sub legendre-array-e(Int $norm, UInt $lmax, Num(Cool) $x where -1 ≤ \* ≤ 1, Num(Cool) $csphase where \* == 1|-1 --> List) is export(:legendre)
  
  These functions calculate all normalized associated Legendre polynomials. The parameter norm specifies the normalization to be used.
  
  ### sub legendre-deriv-array(Int $norm, size\_t $lmax where \* ≤ 150, Num(Cool) $x where -1 ≤ \* ≤ 1 --> List) is export(:legendre)
  
  ### sub legendre-deriv-array-e(Int $norm, UInt $lmax, Num(Cool) $x where -1 ≤ \* ≤ 1, Num(Cool) $csphase where \* == 1|-1 --> List) is export(:legendre)
  
  These functions calculate all normalized associated Legendre functions and their first derivatives up to degree lmax. The parameter norm specifies the normalization to be used. They return a List of Pairs (that can be read as a Hash):
  
  * :out array of Pⁿₗ(x) values
  * :derout array of dPⁿₗ(x)/dx values
  
  ### sub legendre-deriv-alt-array(Int $norm, size\_t $lmax where \* ≤ 150, Num(Cool) $x where -1 ≤ \* ≤ 1 --> List) is export(:legendre)
  
  ### sub legendre-deriv-alt-array-e(Int $norm, UInt $lmax, Num(Cool) $x where -1 ≤ \* ≤ 1, Num(Cool) $csphase where \* == 1|-1 --> List) is export(:legendre)
  
  These functions calculate all normalized associated Legendre functions and their (alternate) first derivatives up to degree lmax. The parameter norm specifies the normalization to be used. To include or exclude the Condon-Shortley phase factor of (−1)ⁿ, set the parameter csphase to either −1 or 1 respectively. They return a List of Pairs (that can be read as a Hash):
  
  * :out array of Pⁿₗ(x) values
  * :derout array of dPⁿₗ(x)/dx values
  
  ### sub legendre-deriv2-array(Int $norm, size\_t $lmax where \* ≤ 150, Num(Cool) $x where -1 ≤ \* ≤ 1 --> List) is export(:legendre)
  
  ### sub legendre-deriv2-array-e(Int $norm, UInt $lmax, Num(Cool) $x where -1 ≤ \* ≤ 1, Num(Cool) $csphase where \* == 1|-1 --> List) is export(:legendre)
  
  These functions calculate all normalized associated Legendre functions and their first and second derivatives up to degree lmax. The parameter norm specifies the normalization to be used. They return a List of Pairs (that can be read as a Hash):
  
  * :out array of Pⁿₗ(x) values
  * :derout array of dPⁿₗ(x)/dx values
  * :derout2 array of d²Pⁿₗ(x)/d²x values
  
  ### sub legendre-deriv2-alt-array(Int $norm, size\_t $lmax where \* ≤ 150, Num(Cool) $x where -1 ≤ \* ≤ 1 --> List) is export(:legendre)
  
  ### sub legendre-deriv2-alt-array-e(Int $norm, UInt $lmax, Num(Cool) $x where -1 ≤ \* ≤ 1, Num(Cool) $csphase where \* == 1|-1 --> List) is export(:legendre)
  
  These functions calculate all normalized associated Legendre functions and their (alternate) first and second derivatives up to degree lmax. The parameter norm specifies the normalization to be used. To include or exclude the Condon-Shortley phase factor of (−1)ⁿ, set the parameter csphase to either −1 or 1 respectively. They return a List of Pairs (that can be read as a Hash):
  
  * :out array of normalized Pⁿₗ(x) values
  * :derout array of dPⁿₗ(cos(θ))/dθ values
  * :derout2 array of d²Pⁿₗ(cos(θ))/d²θ values
  
  ### sub legendre-Plm(UInt $l, UInt $n, Num(Cool) $x where -1 ≤ \* ≤ 1 --> Num) is export(:legendre)
  
  ### sub legendre-Plm-e(UInt $l, UInt $n, Num(Cool) $x where -1 ≤ \* ≤ 1 --> List) is export(:legendre)
  
  These routines compute the associated Legendre polynomial Pⁿₗ(x).
  
  ### sub legendre-sphPlm(UInt $l, UInt $m, Num(Cool) $x where -1 ≤ \* ≤ 1 --> Num) is export(:legendre)
  
  ### sub legendre-sphPlm-e(UInt $l, UInt $m, Num(Cool) $x where -1 ≤ \* ≤ 1 --> List) is export(:legendre)
  
  These routines compute the normalized associated Legendre polynomial.
  
  ### sub conicalP-half(Num(Cool) $lambda, Num(Cool) $x where \* > -1 --> Num) is export(:legendre)
  
  ### sub conicalP-half-e(Num(Cool) $lambda, Num(Cool) $x where \* > -1 --> List) is export(:legendre)
  
  These routines compute the irregular Spherical Conical Function.
  
  ### sub conicalP-mhalf(Num(Cool) $lambda, Num(Cool) $x where \* > -1 --> Num) is export(:legendre)
  
  ### sub conicalP-mhalf-e(Num(Cool) $lambda, Num(Cool) $x where \* > -1 --> List) is export(:legendre)
  
  These routines compute the regular Spherical Conical Function.
  
  ### sub conicalP0(Num(Cool) $lambda, Num(Cool) $x where \* > -1 --> Num) is export(:legendre)
  
  ### sub conicalP0-e(Num(Cool) $lambda, Num(Cool) $x where \* > -1 --> List) is export(:legendre)
  
  These routines compute the conical function P⁰.
  
  ### sub conicalP1(Num(Cool) $lambda, Num(Cool) $x where \* > -1 --> Num) is export(:legendre)
  
  ### sub conicalP1-e(Num(Cool) $lambda, Num(Cool) $x where \* > -1 --> List) is export(:legendre)
  
  These routines compute the conical function P¹.
  
  ### sub conicalP-sph-reg(Int $l where \* ≥ -1, Num(Cool) $lambda, Num(Cool) $x where \* > -1 --> Num) is export(:legendre)
  
  ### sub conicalP-sph-reg-e(Int $l where \* ≥ -1, Num(Cool) $lambda, Num(Cool) $x where \* > -1 --> List) is export(:legendre)
  
  These routines compute the Regular Spherical Conical Function.
  
  ### sub conicalP-cyl-reg(Int $m where \* ≥ -1, Num(Cool) $lambda, Num(Cool) $x where \* > -1 --> Num) is export(:legendre)
  
  ### sub conicalP-cyl-reg-e(Int $m where \* ≥ -1, Num(Cool) $lambda, Num(Cool) $x where \* > -1 --> List) is export(:legendre)
  
  These routines compute the Regular Cylindrical Conical Function.
  
  ### sub legendre-H3d0(Num(Cool) $lambda, Num(Cool) $eta where \* ≥ 0 --> Num) is export(:legendre)
  
  ### sub legendre-H3d0-e(Num(Cool) $lambda, Num(Cool) $eta where \* ≥ 0 --> List) is export(:legendre)
  
  These routines compute the zeroth radial eigenfunction of the Laplacian on the 3-dimensional hyperbolic space.
  
  ### sub legendre-H3d1(Num(Cool) $lambda, Num(Cool) $eta where \* ≥ 0 --> Num) is export(:legendre)
  
  ### sub legendre-H3d1-e(Num(Cool) $lambda, Num(Cool) $eta where \* ≥ 0 --> List) is export(:legendre)
  
  These routines compute the first radial eigenfunction of the Laplacian on the 3-dimensional hyperbolic space.
  
  ### sub legendre-H3d(UInt $l, Num(Cool) $lambda, Num(Cool) $eta where \* ≥ 0 --> Num) is export(:legendre)
  
  ### sub legendre-H3d-e(UInt $l, Num(Cool) $lambda, Num(Cool) $eta where \* ≥ 0 --> List) is export(:legendre)
  
  These routines compute the l-th radial eigenfunction of the Laplacian on the 3-dimensional hyperbolic space.
  
  ### sub legendre-H3d-array(UInt $lmax, Num(Cool) $lambda, Num(Cool) $eta where \* ≥ 0 --> List) is export(:legendre)
  
  This function computes an array of radial eigenfunctions.
  
  ### sub gsl-log(Num(Cool) $x where \* > 0 --> Num) is export(:log)
  
  ### sub gsl-log-e(Num(Cool) $x where \* > 0 --> List) is export(:log)
  
  These routines compute the logarithm of x.
  
  ### sub gsl-log-abs(Num(Cool) $x where \* ≠ 0 --> Num) is export(:log)
  
  ### sub gsl-log-abs-e(Num(Cool) $x where \* ≠ 0 --> List) is export(:log)
  
  These routines compute the logarithm of the magnitude of x.
  
  ### sub gsl-log-complex-e(Num(Cool) $zr, Num(Cool) $zi --> List) is export(:log)
  
  This routine computes the complex logarithm of z = zᵣ + izᵢ. The returned parameters are the radial part, its error, θ in the range [−π, π], and its error.
  
  ### sub gsl-log1plusx(Num(Cool) $x where \* > -1 --> Num) is export(:log)
  
  ### sub gsl-log1plusx-e(Num(Cool) $x where \* > -1 --> List) is export(:log)
  
  These routines compute log(1 + x).
  
  ### sub gsl-log1plusx-mx(Num(Cool) $x where \* > -1 --> Num) is export(:log)
  
  ### sub gsl-log1plusx-mx-e(Num(Cool) $x where \* > -1 --> List) is export(:log)
  
  These routines compute log(1 + x) − x.
  
  ### sub mathieu-a(Int $n, Num(Cool) $q --> Num) is export(:mathieu)
  
  ### sub mathieu-a-e(Int $n, Num(Cool) $q --> List) is export(:mathieu)
  
  ### sub mathieu-b(Int $n, Num(Cool) $q --> Num) is export(:mathieu)
  
  ### sub mathieu-b-e(Int $n, Num(Cool) $q --> List) is export(:mathieu)
  
  These routines compute the characteristic values aₙ(q), bₙ(q) of the Mathieu functions ceₙ(q, x) and seₙ(q, x), respectively.
  
  ### sub mathieu-a-array(Int $order-min, Int $order-max, Num(Cool) $q --> List) is export(:mathieu)
  
  ### sub mathieu-b-array(Int $order-min, Int $order-max, Num(Cool) $q --> List) is export(:mathieu)
  
  These routines compute a series of Mathieu characteristic values aₙ(q), bₙ(q) for n from order\_min to order\_max inclusive.
  
  ### sub mathieu-ce(Int $n, Num(Cool) $q, Num(Cool) $x --> Num) is export(:mathieu)
  
  ### sub mathieu-ce-e(Int $n, Num(Cool) $q, Num(Cool) $x --> List) is export(:mathieu)
  
  ### sub mathieu-se(Int $n, Num(Cool) $q, Num(Cool) $x --> Num) is export(:mathieu)
  
  ### sub mathieu-se-e(Int $n, Num(Cool) $q, Num(Cool) $x --> List) is export(:mathieu)
  
  These routines compute the angular Mathieu functions ceₙ(q, x) and seₙ(q, x), respectively.
  
  ### sub mathieu-ce-array(Int $order-min, Int $order-max, Num(Cool) $q, Num(Cool) $x --> List) is export(:mathieu)
  
  ### sub mathieu-se-array(Int $order-min, Int $order-max, Num(Cool) $q, Num(Cool) $x --> List) is export(:mathieu)
  
  These routines compute a series of the angular Mathieu functions ceₙ(q, x) and seₙ(q, x) of order n from nmin to nmax inclusive.
  
  ### sub mathieu-Mc(Int $j where \* == 1|2, Int $n, Num(Cool) $q, Num(Cool) $x --> Num) is export(:mathieu)
  
  ### sub mathieu-Mc-e(Int $j where \* == 1|2, Int $n, Num(Cool) $q, Num(Cool) $x --> List) is export(:mathieu)
  
  ### sub mathieu-Ms(Int $j where \* == 1|2, Int $n, Num(Cool) $q, Num(Cool) $x --> Num) is export(:mathieu)
  
  ### sub mathieu-Ms-e(Int $j where \* == 1|2, Int $n, Num(Cool) $q, Num(Cool) $x --> List) is export(:mathieu)
  
  These routines compute the radial j-th kind Mathieu functions Mcₙ(q, x) and Msₙ(q, x) of order n.
  
  ### sub mathieu-Mc-array(Int $j where \* == 1|2, Int $nmin, Int $nmax, Num(Cool) $q, Num(Cool) $x --> List) is export(:mathieu)
  
  ### sub mathieu-Ms-array(Int $j where \* == 1|2, Int $nmin, Int $nmax, Num(Cool) $q, Num(Cool) $x --> List) is export(:mathieu)
  
  These routines compute a series of the radial Mathieu functions of kind j, with order from nmin to nmax inclusive.
  
  ### sub pow-int(Num(Cool) $x, Int $n --> Num) is export(:pow)
  
  ### sub pow-int-e(Num(Cool) $x, Int $n --> List) is export(:pow)
  
  These routines compute the power xⁿ for integer n.
  
  ### sub psi-int(UInt $n where \* > 0 --> Num) is export(:psi)
  
  ### sub psi-int-e(UInt $n where \* > 0 --> List) is export(:psi)
  
  These routines compute the Digamma function ψ(n) for positive integer n.
  
  ### sub psi(Num(Cool) $x where \* ≠ 0 --> Num) is export(:psi)
  
  ### sub psi-e(Num(Cool) $x where \* ≠ 0 --> List) is export(:psi)
  
  These routines compute the Digamma function ψ(x) for general x.
  
  ### sub psi1piy(Num(Cool) $y --> Num) is export(:psi)
  
  ### sub psi1piy-e(Num(Cool) $y --> List) is export(:psi)
  
  These routines compute the real part of the Digamma function on the line 1 + iy.
  
  ### sub psi1-int(UInt $n where \* > 0 --> Num) is export(:psi)
  
  ### sub psi1-int-e(UInt $n where \* > 0 --> List) is export(:psi)
  
  These routines compute the Trigamma function ψ’(n) for positive integer n.
  
  ### sub psi1(Num(Cool) $x --> Num) is export(:psi)
  
  ### sub psi1-e(Num(Cool) $x --> List) is export(:psi)
  
  These routines compute the Trigamma function ψ’(x) for general x.
  
  ### sub psin(UInt $n, Num(Cool) $x where \* > 0 --> Num) is export(:psi)
  
  ### sub psin-e(UInt $n, Num(Cool) $x where \* > 0 --> List) is export(:psi)
  
  These routines compute the polygamma function ψ⁽ⁿ⁾(x).
  
  ### sub synchrotron1(Num(Cool) $x where \* ≥ 0 --> Num) is export(:sync)
  
  ### sub synchrotron1-e(Num(Cool) $x where \* ≥ 0 --> List) is export(:sync)
  
  These routines compute the first synchrotron function.
  
  ### sub synchrotron2(Num(Cool) $x where \* ≥ 0 --> Num) is export(:sync)
  
  ### sub synchrotron2-e(Num(Cool) $x where \* ≥ 0 --> List) is export(:sync)
  
  These routines compute the second synchrotron function.
  
  ### sub transport2(Num(Cool) $x where \* ≥ 0 --> Num) is export(:transport)
  
  ### sub transport2-e(Num(Cool) $x where \* ≥ 0 --> List) is export(:transport)
  
  These routines compute the transport function J(2, x).
  
  ### sub transport3(Num(Cool) $x where \* ≥ 0 --> Num) is export(:transport)
  
  ### sub transport3-e(Num(Cool) $x where \* ≥ 0 --> List) is export(:transport)
  
  These routines compute the transport function J(3, x).
  
  ### sub transport4(Num(Cool) $x where \* ≥ 0 --> Num) is export(:transport)
  
  ### sub transport4-e(Num(Cool) $x where \* ≥ 0 --> List) is export(:transport)
  
  These routines compute the transport function J(4, x).
  
  ### sub transport5(Num(Cool) $x where \* ≥ 0 --> Num) is export(:transport)
  
  ### sub transport5-e(Num(Cool) $x where \* ≥ 0 --> List) is export(:transport)
  
  These routines compute the transport function J(5, x).
  
  ### sub gsl-sin(Num(Cool) $x --> Num) is export(:trig)
  
  ### sub gsl-sin-e(Num(Cool) $x --> List) is export(:trig)
  
  These routines compute the sine function sin(x).
  
  ### sub gsl-cos(Num(Cool) $x --> Num) is export(:trig)
  
  ### sub gsl-cos-e(Num(Cool) $x --> List) is export(:trig)
  
  These routines compute the cosine function cos(x).
  
  ### sub gsl-hypot(Num(Cool) $x, Num(Cool) $y --> Num) is export(:trig)
  
  ### sub gsl-hypot-e(Num(Cool) $x, Num(Cool) $y --> List) is export(:trig)
  
  These routines compute the hypotenuse function.
  
  ### sub gsl-sinc(Num(Cool) $x --> Num) is export(:trig)
  
  ### sub gsl-sinc-e(Num(Cool) $x --> List) is export(:trig)
  
  These routines compute sinc(x) = sin(πx)/(πx).
  
  ### sub gsl-complex-sin-e(Num(Cool) $zr, Num(Cool) $zi --> List) is export(:trig)
  
  This function computes the complex sine.
  
  ### sub gsl-complex-cos-e(Num(Cool) $zr, Num(Cool) $zi --> List) is export(:trig)
  
  This function computes the complex cosine.
  
  ### sub gsl-complex-logsin-e(Num(Cool) $zr, Num(Cool) $zi --> List) is export(:trig)
  
  This function computes the logarithm of the complex sine.
  
  ### sub gsl-lnsinh(Num(Cool) $x where \* > 0 --> Num) is export(:trig)
  
  ### sub gsl-lnsinh-e(Num(Cool) $x where \* > 0 --> List) is export(:trig)
  
  These routines compute log(sinh(x)).
  
  ### sub gsl-lncosh(Num(Cool) $x --> Num) is export(:trig)
  
  ### sub gsl-lncosh-e(Num(Cool) $x --> List) is export(:trig)
  
  These routines compute log(cosinh(x)).
  
  ### sub polar-to-rect(Num(Cool) $r, Num(Cool) $θ where -π ≤ \* ≤ π --> List) is export(:trig)
  
  This function converts the polar coordinates (r, θ) to rectilinear coordinates (x, y).
  
  ### sub rect-to-polar(Num(Cool) $x, Num(Cool) $y --> List) is export(:trig)
  
  This function converts the rectilinear coordinates (x, y) to polar coordinates (r, θ).
  
  ### sub angle-restrict-symm(Num(Cool) $θ --> Num) is export(:trig)
  
  ### sub angle-restrict-symm-e(Num(Cool) $θ --> Num) is export(:trig)
  
  These routines force the angle θ to lie in the range (−π, π].
  
  ### sub angle-restrict-pos(Num(Cool) $θ --> Num) is export(:trig)
  
  ### sub angle-restrict-pos-e(Num(Cool) $θ --> Num) is export(:trig)
  
  These routines force the angle θ to lie in the range [0, 2π).
  
  ### sub gsl-sin-err-e(Num(Cool) $x, Num(Cool) $dx --> List) is export(:trig)
  
  This routine computes the sine of an angle x with an associated absolute error dx, sin(x ± dx).
  
  ### sub gsl-cos-err-e(Num(Cool) $x, Num(Cool) $dx --> List) is export(:trig)
  
  This routine computes the cosine of an angle x with an associated absolute error dx, cosin(x ± dx).
  
  ### sub zeta-int(Int $n where \* ≠ 1 --> Num) is export(:zeta)
  
  ### sub zeta-int-e(Int $n where \* ≠ 1 --> List) is export(:zeta)
  
  These routines compute the Riemann zeta function ζ(n).
  
  ### sub zeta(Num(Cool) $s where \* ≠ 1 --> Num) is export(:zeta)
  
  ### sub zeta-e(Num(Cool) $s where \* ≠ 1 --> List) is export(:zeta)
  
  These routines compute the Riemann zeta function ζ(s) for arbitrary s.
  
  ### sub zetam1-int(Int $n where \* ≠ 1 --> Num) is export(:zeta)
  
  ### sub zetam1-int-e(Int $n where \* ≠ 1 --> List) is export(:zeta)
  
  These routines compute ζ(n) − 1 for integer n.
  
  ### sub zetam1(Num(Cool) $s where \* ≠ 1 --> Num) is export(:zeta)
  
  ### sub zetam1-e(Num(Cool) $s where \* ≠ 1 --> List) is export(:zeta)
  
  These routines compute ζ(s) − 1 for arbitrary s.
  
  ### sub hzeta(Num(Cool) $t where \* > 1, Num(Cool) $q where \* > 0 --> Num) is export(:zeta)
  
  ### sub hzeta-e(Num(Cool) $t where \* > 1, Num(Cool) $q where \* > 0 --> List) is export(:zeta)
  
  These routines compute the Hurwitz zeta function ζ(t, q).
  
  ### sub eta-int(Int $n --> Num) is export(:zeta)
  
  ### sub eta-int-e(Int $n --> List) is export(:zeta)
  
  These routines compute the eta function η(n) for integer n.
  
  ### sub eta(Num(Cool) $s --> Num) is export(:zeta)
  
  ### sub eta-e(Num(Cool) $s --> List) is export(:zeta)
  
  These routines compute the eta function η(s) for arbitrary s.
  
  # C Library Documentation
  
  For more details on libgsl see <https://www.gnu.org/software/gsl/>. The excellent C Library manual is available here <https://www.gnu.org/software/gsl/doc/html/index.html>, or here <https://www.gnu.org/software/gsl/doc/latex/gsl-ref.pdf> in PDF format.
  
  # Prerequisites
  
  This module requires the libgsl library to be installed. Please follow the instructions below based on your platform:
  
  ## Debian Linux and Ubuntu 20.04
  
  ```
  sudo apt install libgsl23 libgsl-dev libgslcblas0
  
  ```
  
  That command will install libgslcblas0 as well, since it's used by the GSL.
  
  ## Ubuntu 18.04
  
  libgsl23 and libgslcblas0 have a missing symbol on Ubuntu 18.04. I solved the issue installing the Debian Buster version of those three libraries:
  
  * <http://http.us.debian.org/debian/pool/main/g/gsl/libgslcblas0_2.5+dfsg-6_amd64.deb>
  * <http://http.us.debian.org/debian/pool/main/g/gsl/libgsl23_2.5+dfsg-6_amd64.deb>
  * <http://http.us.debian.org/debian/pool/main/g/gsl/libgsl-dev_2.5+dfsg-6_amd64.deb>
  
  # Installation
  
  To install it using zef (a module management tool):
  
  ```
  $ zef install Math::Libgsl::Function
  
  ```
  
  # AUTHOR
  
  Fernando Santagata [nando.santagata@gmail.com](mailto:nando.santagata@gmail.com)
  
  # COPYRIGHT AND LICENSE
  
  Copyright 2020 Fernando Santagata
  
  This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.
  