### LHAPDF v5/v6 Compatibility Example

Source: https://lhapdf.hepforge.org/_2examples_2compatibility_8cc-example.html

This example demonstrates how to use LHAPDF to retrieve parton density information, with conditional compilation for LHAPDF v5 and v6. It requires the LHAPDF library to be installed.

```cpp
// -*- C++ -*-
// LHAPDFv5/v6 compatibility example
#include "LHAPDF/LHAPDF.h"
#include <iostream>
int main() {
const double x = 1e-3, Q = 200;
#if LHAPDF_MAJOR_VERSION == 6
LHAPDF::PDF* pdf = LHAPDF::mkPDF("CT10nlo", 0);
std::cout << "xf_g = " << pdf->xfxQ(21, x, Q) << std::endl;
delete pdf;
#else
LHAPDF::initPDFSet("CT10nlo", LHAPDF::LHGRID, 0);
std::cout << "xf_g = " << LHAPDF::xfx(x, Q, 0) << std::endl;
#endif
return 0;
}
```

--------------------------------

### Fortran Example: Using PDFs

Source: https://lhapdf.hepforge.org/codeexamples.html

An example Fortran program demonstrating how to initialize PDF sets by name, retrieve PDF information (like xmin, xmax, Q2min, Q2max), and evolve PDFs at different x and Q values.

```APIDOC
## Using PDFs in Fortran

This example demonstrates the usage of LHAPDF in Fortran.

### Program Structure

- Initializes PDF sets by name.
- Retrieves information about available PDF sets.
- Gets range information (xmin, xmax, Q2min, Q2max) for each set.
- Evolves PDFs for various partons (up, down, gluon, etc.) at specified x and Q values.
- Handles sets with and without photon PDFs.

### Key Functions Used:

- `initpdfsetbyname(name)`: Initializes a PDF set using its name.
- `numberpdf()`: Returns the number of available PDF sets.
- `initpdf(i)`: Initializes the i-th PDF set.
- `getxmin(i, xmin)`: Gets the minimum x value for PDF set i.
- `getxmax(i, xmax)`: Gets the maximum x value for PDF set i.
- `getq2min(i, q2min)`: Gets the minimum Q^2 value for PDF set i.
- `getq2max(i, q2max)`: Gets the maximum Q^2 value for PDF set i.
- `getminmax(i, xmin, xmax, q2min, q2max)`: Gets all range information for PDF set i.
- `alphaspdf(qmz)`: Calculates alpha_s at a given scale.
- `getlam4m(1, i, xlam4)`: Retrieves lambda_4 for PDF set i.
- `getlam5m(1, i, xlam5)`: Retrieves lambda_5 for PDF set i.
- `evolvepdf(x, q, f)`: Evolves PDFs for a given x and Q.
- `evolvepdfphoton(x, q, f, photon)`: Evolves PDFs including the photon component.
- `has_photon()`: Checks if the current PDF set includes a photon.

### Example Snippet:

```fortran
program example1
implicit double precision (a-h,o-z)
character name*64
double precision f(-6:6)
character*20 lparm
logical has_photon
dimension z(10), xx(10)
Data (z(i), i=1,10) /.05, .1, .2, .3, .4, .5, .6, .7, .8, .9/
Do i = 1, 10
xx(i) = z(i) **3
EndDo
name='CT10nlo.LHgrid'
call initpdfsetbyname(name)
qmz=91.18d0
call numberpdf(n)
print *,'There are ',n,' PDF sets'
do i=0,n
call initpdf(i)
write(*,*) 'PDF set ',i
call getminmax(i,xmin,xmax,q2min,q2max)
print *,'xmin=',xmin,' xmax=',xmax,' Q2min=',q2min,' Q2max=',q2max
write(*,*) 
a=alphaspdf(qmz)
write(*,*) 'alpha_S(M_Z) = ',a
call getlam5m(1,i,xlam5)
print *,' lambda5: ',xlam5
write(*,*) 
write(*,*) 'x*up'
write(*,*) ' x Q=10 GeV Q=100 GeV Q=1000 GeV'
q = 50.0d0
print *,q
do ix=1,10
x = xx(ix)
if(has_photon()) then
print *,"This set has a photon"
call evolvepdfphoton(x,q,f,photon)
else
call evolvepdf(x,q,f)
endif
g = f(0)
u = f(2)
d = f(1)
write(*,'(F7.4,13(1pE10.3))') x,u,d,g
enddo
enddo
end program example1
```
```

--------------------------------

### Configure Runtime Environment Variables

Source: https://lhapdf.hepforge.org/install.html

Example of setting PATH, LD_LIBRARY_PATH, and PYTHONPATH to point to a custom LHAPDF installation directory.

```bash
export PATH=$PATH:/foo/lhapdf/bin
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/foo/lhapdf/lib
export PYTHONPATH=$PYTHONPATH:/foo/lhapdf/lib/python3.9/site-packages
```

--------------------------------

### Build and Install LHAPDF from Source

Source: https://lhapdf.hepforge.org/install.html

Standard sequence of commands to download, configure, and install the LHAPDF library on a system with a C++11 compiler.

```bash
wget https://lhapdf.hepforge.org/downloads/?f=LHAPDF-6.X.Y.tar.gz -O LHAPDF-6.X.Y.tar.gz
# ^ or use a web browser to download, which will get the filename correct
tar xf LHAPDF-6.X.Y.tar.gz
cd LHAPDF-6.X.Y
./configure --prefix=/path/for/installation
make
make install
```

--------------------------------

### Install via Fedora dnf

Source: https://lhapdf.hepforge.org/install.html

Install LHAPDF and development headers using dnf.

```bash
sudo dnf install lhapdf lhapdf-devel python3-lhapdf
```

--------------------------------

### AnalyticPDF Example

Source: https://lhapdf.hepforge.org/codeexamples.html

Example of creating a custom PDF subclass in C++.

```APIDOC
## AnalyticPDF C++ Example

### Description
This example demonstrates how to create a custom PDF subclass named `AnalyticPDF` by inheriting from `LHAPDF::PDF` and implementing the necessary virtual functions.

### Code Structure
```cpp
#include "LHAPDF/PDF.h"
#include <iostream>

struct AnalyticPDF : public LHAPDF::PDF {
  AnalyticPDF() {
    info().set_entry("Flavors", "-5,-4,-3,-2,-1,21,1,2,3,4,5");
  }

  double _xfxQ2(int id, double x, double q2) const override {
    if (abs(id) > 5 && id != 21) return 0;
    return 0.15 * sin(20.0*x) * sin(20.0*q2);
  }

  void _xfxQ2(double x, double q2, std::vector<double>& ret) const override {
    for (int id(-5); id<5; ++id)
      _xfxQ2(id,x,q2);
  }

  bool inRangeX(double x) const override { return true; }
  bool inRangeQ2(double q2) const override { return true; }
};

int main(int argc, const char* argv[]) {
  AnalyticPDF apdf;
  LHAPDF::PDF& pdf = apdf;
  for (double x = 0; x < 1.0; x += 0.1) {
    for (double logq2 = 1; logq2 < 6; logq2 += 0.5) {
      const double q2 = pow(10, logq2);
      std::cout << x << " " << q2 << " " << pdf.xfxQ2(21, x, q2) << std::endl;
    }
  }
  return 0;
}
```

### Usage
Compile and run the C++ code. The `main` function iterates through various `x` and `q2` values, calculating and printing the PDF value for the gluon (id=21) using the custom `AnalyticPDF` implementation.
```

--------------------------------

### Install via OpenSUSE zypper

Source: https://lhapdf.hepforge.org/install.html

Install LHAPDF using the OpenSUSE package manager.

```bash
sudo zypper install lhapdf
```

--------------------------------

### Install via Gentoo emerge

Source: https://lhapdf.hepforge.org/install.html

Install LHAPDF using the Gentoo package manager.

```bash
sudo emerge --ask lhapdf
```

--------------------------------

### Configure LHAPDF build

Source: https://lhapdf.hepforge.org/install.html

Set up the build environment by specifying the installation prefix.

```bash
./configure --prefix=$HOME/local
```

--------------------------------

### Check LHAPDF Version and Data Directory via LCG

Source: https://lhapdf.hepforge.org/install.html

After sourcing the LCG setup script, verify the installed LHAPDF version and query the default data directory using `lhapdf --version` and `lhapdf-config --datadir`.

```bash
~ $ lhapdf --version
6.5.3
~ $ lhapdf-config --datadir
/cvmfs/sft.cern.ch/lcg/releases/MCGenerators/lhapdf/6.5.3-642a8/x86_64-ubuntu2004-gcc9-opt/share/LHAPDF
```

--------------------------------

### AnalyticPDF Example Implementation

Source: https://lhapdf.hepforge.org/_2examples_2analyticpdf_8cc-example.html

An example implementation of an analytic PDF using the LHAPDF::PDF interface.

```APIDOC
## struct AnalyticPDF : public LHAPDF::PDF

### Description
An example implementation of an analytic PDF that inherits from `LHAPDF::PDF`.

### Constructor
`AnalyticPDF()`
Initializes the PDF with specific flavor information.

### Methods

#### `double _xfxQ2(int id, double x, double q2) const`
Calculates the PDF xf(x) value at (x,q2) for the given PID using an analytic formula.

#### `void _xfxQ2(double x, double q2, std::vector<double>& ret) const`
Calculates PDF values for multiple PIDs at a given (x,q2).

#### `bool inRangeX(double x) const`
Always returns true, indicating x is always in range.

#### `bool inRangeQ2(double q2) const`
Always returns true, indicating Q2 is always in range.

### Example Usage
```cpp
#include "LHAPDF/PDF.h"
#include <iostream>

struct AnalyticPDF : public LHAPDF::PDF {
  AnalyticPDF() {
    info().set_entry("Flavors", "-5,-4,-3,-2,-1,21,1,2,3,4,5");
  }
  double _xfxQ2(int id, double x, double q2) const {
    if (abs(id) > 5 && id != 21) return 0;
    return 0.15 * sin(20.0*x) * sin(20.0*q2);
  }
  void _xfxQ2(double x, double q2, std::vector<double>& ret) const {
    for (int id(-5); id<5; ++id)
      _xfxQ2(id,x,q2);
  }
  bool inRangeX(double x) const { return true; }
  bool inRangeQ2(double q2) const { return true; }
};

int main(int argc, const char* argv[]) {
  AnalyticPDF apdf;
  LHAPDF::PDF& pdf = apdf;
  for (double x = 0; x < 1.0; x += 0.1) {
    for (double logq2 = 1; logq2 < 6; logq2 += 0.5) {
      const double q2 = pow(10, logq2);
      std::cout << x << " " << q2 << " " << pdf.xfxQ2(21, x, q2) << std::endl;
    }
  }
  return 0;
}
```
```

--------------------------------

### Get Ordered List of Search Paths

Source: https://lhapdf.hepforge.org/Paths_8h_source.html

Retrieves the ordered list of search paths, which includes the $LHAPDF_DATA_PATH environment variable and the default install location. The install prefix is appended unless $LHAPDF_DATA_PATH ends with '::'.

```cpp
#include "LHAPDF/Utils.h"

namespace LHAPDF {


/// @brief Get the ordered list of search paths, from $LHAPDF_DATA_PATH and the install location
/// @note The install prefix will be appended *unless* $LHAPDF_DATA_PATH ends with a double colon, i.e. '::'
std::vector<std::string> paths();

}
```

--------------------------------

### Install via Homebrew on macOS

Source: https://lhapdf.hepforge.org/install.html

Add the homebrew-hep tap and install LHAPDF.

```bash
brew tap davidchall/hep
brew install lhapdf
```

--------------------------------

### Install via Arch Linux pacman

Source: https://lhapdf.hepforge.org/install.html

Install the required dependencies using the Arch Linux package manager.

```bash
sudo pacman -Syu hepmc
```

--------------------------------

### Calculate alpha_s and manage PDF resources

Source: https://lhapdf.hepforge.org/_2tests_2testalphas_8cc-example.html

Example usage of alpha_s calculation methods and cleanup of PDF objects.

```cpp
<< " num flavs = " << as_ode.numFlavorsQ(q) << endl;
fo << q << " " << as_ode_q << endl;
// const double as_ipol_q = as_ipol.alphasQ(q);
// cout << "Interpolated solution: " << setprecision(3) << setw(6) << ( (as_ipol_q > 2) ? inf : as_ipol_q ) << endl;
// fi << q << " " << as_ipol_q << endl;
// const double as_ct10_q = pdf->alphasQ(q);
// cout << "CT10 solution: " << setprecision(3) << setw(6) << as_ct10_q << endl;
// fc << q << " " << as_ct10_q << endl;
// const double as_ct10_q_2 = pdf->alphaS().alphasQ(q);
// cout << "CT10 AlphaS solution: " << setprecision(3) << setw(6) << as_ct10_q_2
// << " agrees = " << boolalpha << (as_ct10_q == as_ct10_q_2) << endl;
// cout << endl;
}
fa.close(); fo.close(); fi.close(); fc.close();
delete pdf;
#ifdef HAVE_MPI
MPI_Finalize();
#endif 
return 0;
}
```

--------------------------------

### Test LHAPDF Info System

Source: https://lhapdf.hepforge.org/_2tests_2testinfo_8cc-example.html

Example program demonstrating how to access global configuration, PDF set metadata, and individual PDF member information.

```cpp
// Example program for testing the info system
#include "LHAPDF/Info.h"
#include "LHAPDF/Config.h"
#include "LHAPDF/PDFInfo.h"
#include "LHAPDF/PDFSet.h"
#include "LHAPDF/Factories.h"
#include <iostream>
#ifdef HAVE_MPI
#include <mpi.h>
#endif
using namespace std;
int main(int argc, char* argv[]) {
#ifdef HAVE_MPI
MPI_Init(&argc, &argv);
#endif
LHAPDF::Info& cfg = LHAPDF::getConfig();
// cout << "UndefFlavorAction: " << cfg.get_entry("UndefFlavorAction") << endl;
cout << "Verbosity: " << cfg.get_entry("Verbosity") << endl;
cfg.set_entry("Verbosity", 5);
const LHAPDF::Info& cfg2 = LHAPDF::getConfig();
cout << "New Verbosity from second Config: " << cfg2.get_entry("Verbosity") << endl;
const LHAPDF::PDFSet set("CT10nlo");
cout << "SetDesc: " << set.get_entry("SetDesc") << endl;
cout << "Verbosity from set: " << set.get_entry("Verbosity") << endl;
const LHAPDF::PDFInfo info("CT10nlo", 2);
if (info.has_key("PdfDesc")) cout << "PdfDesc: " << info.get_entry("PdfDesc") << endl;
cout << "PdfType: " << info.get_entry("PdfType") << endl;
cout << "Verbosity from PDF: " << info.get_entry("Verbosity") << endl;
vector<int> pids = info.get_entry_as< vector<int> >("Flavors");
cout << "PIDs (1): "; for (int f : pids) { cout << f << " "; } cout << endl;
cout << "PIDs (2): " << LHAPDF::to_str(pids) << endl;
// Now test loading of all central PDFs
for (const string& name : LHAPDF::availablePDFSets()) {
cout << "Testing PDFInfo for " << name << endl;
LHAPDF::PDFInfo* i = LHAPDF::mkPDFInfo(name, 0);
i->has_key("Foo"); // < Force loading of all info levels
delete i;
}
#ifdef HAVE_MPI
MPI_Finalize();
#endif
return 0;
}
```

--------------------------------

### Initialize and Query PDF Sets

Source: https://lhapdf.hepforge.org/_2examples_2pythonexample_8py-example.html

Demonstrates loading PDF sets, querying xfx values, and iterating over flavors.

```python
#! /usr/bin/env python



import lhapdf


p = lhapdf.mkPDF("CT10nlo", 0)
p = lhapdf.mkPDF("CT10nlo/0")


print(p.xfxQ2(21, 1e-3, 1e4))


for pid in p.flavors():
 print(p.xfxQ(pid, 0.01, 91.2))

# TODO: demonstrate looping over PDF set members
pset = lhapdf.getPDFSet("CT10nlo")
print(pset.description)
pcentral = pset.mkPDF(0)
pdfs1 = pset.mkPDFs()
pdfs2 = lhapdf.mkPDFs("CT10nlo") # a direct way to get all the set's PDFs


import numpy as np
xs = [x for x in np.logspace(-7, 0, 5)]
qs = [q for q in np.logspace(1, 4, 4)]
gluon_xfs = np.empty([len(xs), len(qs)])
for ix, x in enumerate(xs):
 for iq, q in enumerate(qs):
 gluon_xfs[ix,iq] = p.xfxQ(21, x, q)
print(gluon_xfs)


print(lhapdf.version())
print(lhapdf.__version__)
lhapdf.pathsPrepend("/path/to/extra/pdfsets")
print(lhapdf.paths())
# ...
```

--------------------------------

### Initialize and Evolve PDFs in Fortran

Source: https://lhapdf.hepforge.org/codeexamples.html

Demonstrates loading a PDF set by name, iterating through members, and evolving the PDF to obtain parton distributions at specific x and Q values.

```Fortran
program example1
implicit double precision (a-h,o-z)
character name*64
double precision f(-6:6)
character*20 lparm
logical has_photon
dimension z(10), xx(10)
Data (z(i), i=1,10) /.05, .1, .2, .3, .4, .5, .6, .7, .8, .9/
Do i = 1, 10
xx(i) = z(i) **3
EndDo
name='CT10nlo.LHgrid'
! name='cteq6.LHgrid'
! name='cteq65.LHgrid'
! name='cteq66.LHgrid'
! name='MRST2006nnlo.LHgrid'
! name='MRST2001E.LHgrid'
! name='H12000ms.LHgrid'
call initpdfsetbyname(name)
qmz=91.18d0
write(*,*)
call numberpdf(n)
print *,'There are ',n,' PDF sets'
do i=0,n
write(*,*) '---------------------------------------------'
call initpdf(i)
write(*,*) 'PDF set ',i
call getxmin(i,xmin)
call getxmax(i,xmax)
call getq2min(i,q2min)
call getq2max(i,q2max)
print *,'xmin=',xmin,' xmax=',xmax,' Q2min=',q2min,' Q2max=',q2max
call getminmax(i,xmin,xmax,q2min,q2max)
print *,'xmin=',xmin,' xmax=',xmax,' Q2min=',q2min,' Q2max=',q2max
call setlhaparm('EXTRAPOLATE') !< These work, but have no effect
call getlhaparm(18,lparm) !< These work, but have no effect
print *,'lhaparm(18)=',lparm
write(*,*)
a=alphaspdf(qmz)
write(*,*) 'alpha_S(M_Z) = ',a
call getlam4m(1,i,xlam4)
call getlam5m(1,i,xlam5)
print *,' lambda5: ',xlam5, ' lambda4: ',xlam4
write(*,*)
write(*,*) 'x*up'
write(*,*) ' x Q=10 GeV Q=100 GeV Q=1000 GeV'
! q2 = 10.0d0
! q = dsqrt(q2)
q = 50.0d0
print *,q
do ix=1,10
! x = (ix-0.5d0)/10.0d0
x = xx(ix)
! x = z(ix)
if(has_photon()) then
print *,"This set has a photon"
call evolvepdfphoton(x,q,f,photon)
else
call evolvepdf(x,q,f)
endif
g = f(0)
u = f(2)
d = f(1)
s = f(3)
c = f(4)
b = f(5)
ubar = f(-2)
dbar = f(-1)
sbar = f(-3)
cbar = f(-4)
bbar = f(-5)
write(*,'(F7.4,13(1pE10.3))') x,u,d,ubar,dbar,s,sbar,c,cbar,b,bbar,g,photon
enddo
enddo
end program example1
```

--------------------------------

### Testing the path searching system in C++

Source: https://lhapdf.hepforge.org/codeexamples.html

Demonstrates how to list configured search paths, find specific files, and list available PDF sets.

```cpp
// Test program for path searching machinery
#include "LHAPDF/Paths.h"
#include <iostream>
using namespace std;
#ifdef HAVE_MPI
#include <mpi.h>
#endif
int main(int argc, char* argv[]) {
#ifdef HAVE_MPI
MPI_Init(&argc, &argv);
#endif
for (const string& p : LHAPDF::paths())
cout << p << endl;
cout << "@" << LHAPDF::findFile("lhapdf.conf") << "@" << endl;
cout << "List of available PDFs:" << endl;
for (const string& s : LHAPDF::availablePDFSets())
cout << " " << s << endl;
#ifdef HAVE_MPI
MPI_Finalize();
#endif
return 0;
}
```

--------------------------------

### Query and Configure PDFs in Python

Source: https://lhapdf.hepforge.org/codeexamples.html

Shows how to instantiate PDF objects, query values using xfxQ, and manage PDF search paths.

```Python
#! /usr/bin/env python
import lhapdf
p = lhapdf.mkPDF("CT10nlo", 0)
p = lhapdf.mkPDF("CT10nlo/0")
print(p.xfxQ2(21, 1e-3, 1e4))
for pid in p.flavors():
print(p.xfxQ(pid, 0.01, 91.2))
# TODO: demonstrate looping over PDF set members
pset = lhapdf.getPDFSet("CT10nlo")
print(pset.description)
pcentral = pset.mkPDF(0)
pdfs1 = pset.mkPDFs()
pdfs2 = lhapdf.mkPDFs("CT10nlo") # a direct way to get all the set's PDFs
import numpy as np
xs = [x for x in np.logspace(-7, 0, 5)]
qs = [q for q in np.logspace(1, 4, 4)]
gluon_xfs = np.empty([len(xs), len(qs)])
for ix, x in enumerate(xs):
for iq, q in enumerate(qs):
gluon_xfs[ix,iq] = p.xfxQ(21, x, q)
print(gluon_xfs)
print(lhapdf.version())
print(lhapdf.__version__)
lhapdf.pathsPrepend("/path/to/extra/pdfsets")
print(lhapdf.paths())
```

--------------------------------

### Setup and Test AlphaS Solvers

Source: https://lhapdf.hepforge.org/codeexamples.html

Initializes and configures three AlphaS solvers: AlphaS_Analytic, AlphaS_ODE, and AlphaS_Ipol. Demonstrates setting QCD order, quark masses, and lambda values for each solver. This snippet is useful for understanding the basic configuration of these solvers.

```C++
#include "LHAPDF/LHAPDF.h"
#include <iostream>
#include <fstream>
#include <limits>
#ifdef HAVE_MPI
#include <mpi.h>
#endif
using namespace LHAPDF;
using namespace std;
int main(int argc, char* argv[]) {
#ifdef HAVE_MPI
MPI_Init(&argc, &argv);
#endif
// Set up three standalone AlphaS solvers:
AlphaS_Analytic as_ana;
// Can set order of QCD (up to 4)
// 0 returns a constant value -- needs to be set by as_ana.setAlphaSMZ(double value);
as_ana.setOrderQCD(4);
// Set quark masses for evolution (both transition points and gradients by default)
as_ana.setQuarkMass(1, 0.0017);
as_ana.setQuarkMass(2, 0.0041);
as_ana.setQuarkMass(3, 0.1);
as_ana.setQuarkMass(4, 1.29);
as_ana.setQuarkMass(5, 4.1);
as_ana.setQuarkMass(6, 172.5);
as_ana.setLambda(3, 0.339);
as_ana.setLambda(4, 0.296);
as_ana.setLambda(5, 0.213);
// Can override quark masses for Nf transitions thresholds by setting them explicitly
// You can't mix the two: if you set one flavor threshold explicitly you need to set all of them.
//as_ode.setQuarkThreshold(6, 650);
//as_ode.setQuarkThreshold(5, 10);
//as_ode.setQuarkThreshold(4, 2);
//as_ode.setQuarkThreshold(3, 0.3);
//as_ode.setQuarkThreshold(2, 0.1);
//as_ode.setQuarkThreshold(1, 0.08);
// Uncomment to use fixed flavor scheme for analytic solver
// as_ana.setFlavorScheme(AlphaS::FIXED, 5);
AlphaS_ODE as_ode;
// As above: order = 0 returns
// constant value set by
// as_ode.setAlphaSMZ(double value);
as_ode.setOrderQCD(5);
as_ode.setMZ(91);
as_ode.setAlphaSMZ(0.118);
// as_ode.setMassReference(4.1);
// as_ode.setAlphaSReference(0.21);
as_ode.setQuarkMass(1, 0.0017);
as_ode.setQuarkMass(2, 0.0041);
as_ode.setQuarkMass(3, 0.1);
as_ode.setQuarkMass(4, 1.29);
as_ode.setQuarkMass(5, 4.1);
as_ode.setQuarkMass(6, 172.5);
// Can override quark masses for Nf transitions thresholds by setting them explicitly
// You can't mix the two: if you set one flavor threshold explicitly you need to set all of them.
// as_ode.setQuarkThreshold(6, 650);
// as_ode.setQuarkThreshold(5, 10);
// as_ode.setQuarkThreshold(4, 2);
// as_ode.setQuarkThreshold(3, 0.3);
// as_ode.setQuarkThreshold(2, 0.1);
// as_ode.setQuarkThreshold(1, 0.08);
// Uncomment to use fixed flavor scheme for ODE solver
// as_ode.setFlavorScheme(AlphaS::FIXED, 4);
AlphaS_Ipol as_ipol;
vector<double> qs = { 1.300000e+00, 1.300000e+00, 1.560453e+00, 1.873087e+00, 2.248357e+00, 2.698811e+00, 3.239513e+00, 3.888544e+00, 4.667607e+00, 5.602754e+00, 6.725257e+00, 8.072650e+00, 9.689992e+00, 1.163137e+01, 1.396169e+01, 1.675889e+01, 2.011651e+01, 2.414681e+01, 2.898459e+01, 3.479160e+01, 4.176203e+01, 5.012899e+01, 6.017224e+01, 7.222765e+01, 8.669834e+01, 1.040682e+02, 1.249181e+02, 1.499452e+02, 1.799865e+02, 2.160465e+02, 2.593310e+02, 3.112875e+02, 3.736534e+02, 4.485143e+02, 5.383733e+02, 6.462355e+02, 7.757077e+02, 9.311194e+02, 1.117668e+03, 1.341590e+03, 1.610376e+03, 1.933012e+03, 2.320287e+03, 2.785153e+03, 3.343154e+03, 4.012949e+03, 4.816936e+03, 4.816936e+03 };
vector<double> alphas = { 4.189466e-01, 4.189466e-01, 3.803532e-01, 3.482705e-01, 3.211791e-01, 2.979983e-01, 2.779383e-01, 2.604087e-01, 2.451922e-01, 2.324903e-01, 2.210397e-01, 2.106640e-01, 2.012187e-01, 1.925841e-01, 1.846600e-01, 1.773623e-01, 1.706194e-01, 1.643704e-01, 1.585630e-01, 1.531520e-01, 1.480981e-01, 1.433671e-01, 1.389290e-01, 1.347574e-01, 1.308290e-01, 1.271232e-01, 1.236215e-01, 1.203076e-01, 1.171667e-01, 1.141857e-01, 1.113525e-01, 1.086566e-01, 1.060881e-01, 1.036382e-01, 1.012990e-01, 9.906295e-02, 9.692353e-02, 9.487457e-02, 9.291044e-02, 9.102599e-02, 8.921646e-02, 8.747747e-02, 8.580498e-02, 8.419524e-02, 8.264479e-02, 8.115040e-02, 7.970910e-02, 7.970910e-02 };
as_ipol.setQValues(qs);
as_ipol.setAlphaSValues(alphas);
// Can interpolate ODE with given knots in Q
// as_ode.setQValues(qs);
// Test these solvers and the CT10nlo PDF's default behaviours:
PDF* pdf = mkPDF("CT10", 0);
const double inf = numeric_limits<double>::infinity();
ofstream fa("alphas_ana.dat"), fo("alphas_ode.dat"), fi("alphas_ipol.dat"), fc("alphas_ct10nlo.dat");
cout << endl;
for (double log10q = -0.5; log10q < 3; log10q += 0.05) {
const double q = pow(10, log10q);
const double as_ana_q = as_ana.alphasQ(q);
cout << fixed;
cout << "Q = " << setprecision(3) << q << " GeV" << endl;
cout << "Analytical solution: " << setprecision(3) << setw(6) << ( (as_ana_q > 2) ? inf : as_ana_q )
<< " num flavs = " << as_ana.numFlavorsQ(q) << endl;
fa << q << " " << as_ana_q << endl;
const double as_ode_q = as_ode.alphasQ(q);
cout << "ODE solution: " << setprecision(3) << setw(6) << ( (as_ode_q > 2) ? inf : as_ode_q )
<< " num flavs = " << as_ode.numFlavorsQ(q) << endl;
fo << q << " " << as_ode_q << endl;
// const double as_ipol_q = as_ipol.alphasQ(q);
// cout << "Interpolated solution: " << setprecision(3) << setw(6) << ( (as_ipol_q > 2) ? inf : as_ipol_q ) << endl;
// fi << q << " " << as_ipol_q << endl;
}

```

--------------------------------

### Print Set Summary

Source: https://lhapdf.hepforge.org/PDFSet_8h_source.html

Prints a summary of the set configuration.

```cpp
void print(std::ostream& os=std::cout, int verbosity=1) const;
```

--------------------------------

### C++ Example: Test PDF Grid Reading and Interpolation

Source: https://lhapdf.hepforge.org/codeexamples.html

This program tests PDF grid format reading and interpolation. It loads a specified PDF set, accesses its metadata, and demonstrates interpolation using xfxQ and xfxQ2 functions. It also writes interpolated data to 'pdf.dat'.

```cpp
#include "LHAPDF/GridPDF.h"
#include <iostream>
#include <fstream>
#ifdef HAVE_MPI
#include <mpi.h>
#endif
using namespace std;
void safeprint(const LHAPDF::PDF& pdf, const string& key) {
if (pdf.info().has_key(key))
cout << key << " = " << pdf.info().get_entry(key) << endl;
}
int main(int argc, char* argv[]) {
#ifdef HAVE_MPI
MPI_Init(&argc, &argv);
#endif
if (argc < 2) {
cout << "Usage: testgrid <PDFNAME=CT10nlo>" << endl;
//exit(1);
}
const string setname = (argc < 2) ? "CT10nlo" : argv[1];
const LHAPDF::PDF* basepdf = LHAPDF::mkPDF(setname);
const LHAPDF::GridPDF& pdf = * dynamic_cast<const LHAPDF::GridPDF*>(basepdf);
for (const string& p : LHAPDF::paths()) cout << p << " : ";
cout << endl;
safeprint(pdf, "Verbosity");
safeprint(pdf, "PdfDesc");
safeprint(pdf, "SetDesc");
cout << "Flavors (str) = " << pdf.info().get_entry("Flavors") << endl;
vector<int> pids = pdf.info().get_entry_as< vector<int> >("Flavors");
cout << "Flavors (ints) = ";
for (int f : pids) cout << f << " ";
cout << endl;
cout << "Flavors (vec<int>) = " << LHAPDF::to_str(pids) << endl;
cout << "x0, Q0 = " << pdf.knotarray().xf(21, 0, 0) << endl;
cout << "x1, Q0 = " << pdf.knotarray().xf(21, 1, 0) << endl;
cout << "x0, Q1 = " << pdf.knotarray().xf(21, 0, 1) << endl;
cout << "x1, Q1 = " << pdf.knotarray().xf(21, 1, 1) << endl;
cout << pdf.xfxQ(21, 0.7, 10.0) << endl;
cout << pdf.xfxQ(21, 0.2, 126) << endl;
for (int pid : pdf.flavors()) {
cout << pid << " = " << pdf.xfxQ(pid, 0.2, 124) << endl;
}
ofstream f("pdf.dat");
for (double x = 0; x <= 1; x += 0.02) {
for (double log10q2 = 1; log10q2 < 5; log10q2 += 0.05) {
f << x << " " << log10q2 << " " << pdf.xfxQ2(21, x, pow(10, log10q2)) << endl;
}
}
f.close();
cout << endl;
#ifdef HAVE_MPI
MPI_Finalize();
#endif
return 0;
}
```

--------------------------------

### Create PDF Grids with creategrids

Source: https://lhapdf.hepforge.org/migration.html

Use this command to create .info and .lha files for a given PDF set. Ensure LHAPDF5 is installed with its Python module.

```bash
./creategrids CT10.LHgrid
```

--------------------------------

### LHAPDF::Extrapolator::pdf

Source: https://lhapdf.hepforge.org/Extrapolator_8h_source.html

Get the associated GridPDF.

```APIDOC
## LHAPDF::Extrapolator::pdf

### Description
Get the associated GridPDF.

### Method
const GridPDF& pdf() const

### Definition
Extrapolator.h:40
```

--------------------------------

### LHAPDF::PDF::set

Source: https://lhapdf.hepforge.org/PDF_8h_source.html

Gets the PDF set of which this PDF is a member.

```APIDOC
## GET /api/pdf/set

### Description
Get the PDF set of which this is a member.

### Method
GET

### Endpoint
/api/pdf/set

### Response
#### Success Response (200)
- **pdf_set** (PDFSet&) - Reference to the PDFSet object.

#### Response Example
```json
{
  "pdf_set": "<PDFSet object details>"
}
```
```

--------------------------------

### LHAPDF::PDF::orderQCD

Source: https://lhapdf.hepforge.org/PDF_8h_source.html

Gets the order of QCD at which this PDF was constructed.

```APIDOC
## GET /api/pdf/orderQCD

### Description
Order of QCD at which this PDF has been constructed.

### Method
GET

### Endpoint
/api/pdf/orderQCD

### Response
#### Success Response (200)
- **order** (int) - The order of QCD.

#### Response Example
```json
{
  "order": 2
}
```
```

--------------------------------

### GET /LHAPDF/version

Source: https://lhapdf.hepforge.org/Version_8h_source.html

Retrieves the current version string of the LHAPDF library.

```APIDOC
## GET /LHAPDF/version

### Description
Returns the current version of the LHAPDF library as a string.

### Method
GET

### Response
#### Success Response (200)
- **version** (string) - The version string of the library (e.g., "6.5.5").

#### Response Example
"6.5.5"
```

--------------------------------

### GET /LHAPDF/verbosity

Source: https://lhapdf.hepforge.org/Config_8h_source.html

Retrieves the current verbosity level of the LHAPDF system.

```APIDOC
## GET /LHAPDF/verbosity

### Description
Returns the current verbosity level. Levels are defined as: 0=silent, 1=standard, 2=debug.

### Method
GET

### Endpoint
LHAPDF::verbosity()

### Response
#### Success Response (200)
- **level** (int) - The current verbosity level (0, 1, or 2).
```

--------------------------------

### Initialize EESSI Environment and Load LHAPDF

Source: https://lhapdf.hepforge.org/install.html

Source the EESSI environment script to set up the necessary paths and modules, then load the LHAPDF package. This prepares your shell to use LHAPDF from the EESSI repository.

```bash
~ $ source /cvmfs/software.eessi.io/versions/2023.06/init/bash
Found EESSI repo @ /cvmfs/software.eessi.io/versions/2023.06!
archdetect says x86_64/intel/haswell
Using x86_64/intel/haswell as software subdirectory.
Using /cvmfs/software.eessi.io/versions/2023.06/software/linux/x86_64/intel/haswell/modules/all as the directory to be added to MODULEPATH.
Found Lmod configuration file at /cvmfs/software.eessi.io/versions/2023.06/software/linux/x86_64/intel/haswell/.lmod/lmodrc.lua
Initializing Lmod...
Prepending /cvmfs/software.eessi.io/versions/2023.06/software/linux/x86_64/intel/haswell/modules/all to $MODULEPATH...
Environment set up to use EESSI (2023.06), have fun!
{EESSI 2023.06} ~ $ module load LHAPDF
```