Add new C++ program to display orders in a grid

examples/cpp/Makefile

@@ -3,20 +3,24 @@ CXXFLAGS = -std=c++11 -O3 -Wall -Wextra
 PINEAPPL_DEPS != pkg-config --cflags --libs pineappl_capi
 LHAPDF_DEPS != pkg-config --cflags --libs lhapdf
 
-all: convolute-grid display-channels fill-custom-grid fill-grid
+all: convolute-grid display-channels display-orders fill-custom-grid fill-grid
 
-test-examples: convolute-grid display-channels fill-custom-grid fill-grid
+test-examples: convolute-grid display-channels display-orders fill-custom-grid fill-grid
 	./fill-grid
 	./fill-custom-grid
 	./convolute-grid
 	./display-channels
+	./display-orders
 
 convolute-grid: convolute-grid.cpp
 	$(CXX) $(CXXFLAGS) $< $(LHAPDF_DEPS) $(PINEAPPL_DEPS) -o $@
 
 display-channels: display-channels.cpp
 	$(CXX) $(CXXFLAGS) $< $(PINEAPPL_DEPS) -o $@
 
+display-orders: display-orders.cpp
+	$(CXX) $(CXXFLAGS) $< $(PINEAPPL_DEPS) -o $@
+
 fill-custom-grid: fill-grid.cpp
 	$(CXX) $(CXXFLAGS) $< -DUSE_CUSTOM_GRID_PARAMETERS $(PINEAPPL_DEPS) -o $@
 
@@ -26,4 +30,4 @@ fill-grid: fill-grid.cpp
 PHONY: clean
 
 clean:
-	rm -f convolute-grid display-channels fill-custom-grid fill-grid
+	rm -f convolute-grid display-channels display-orders fill-custom-grid fill-grid

examples/cpp/display-orders.cpp

@@ -0,0 +1,52 @@
+#include <pineappl_capi.h>
+
+#include <cstddef>
+#include <cstdint>
+#include <iomanip>
+#include <iostream>
+#include <string>
+#include <vector>
+
+int main(int argc, char* argv[]) {
+    std::string filename = "drell-yan-rap-ll.pineappl.lz4";
+
+    switch (argc) {
+    case 2:
+        filename = argv[1];
+    case 1:
+        break;
+
+    default:
+        std::cout << "Usage: " << argv[0] << " [grid]\n";
+    }
+
+    // read the grid from a file
+    auto* grid = pineappl_grid_read(filename.c_str());
+
+    // how many perturbative orders does this grid contain?
+    std::size_t orders = pineappl_grid_order_count(grid);
+
+    std::vector<std::uint32_t> order_params(4 * orders);
+
+    // read out all exponents of the perturbative orders in the grid
+    pineappl_grid_order_params(grid, order_params.data());
+
+    for (std::size_t order = 0; order != orders; ++order) {
+        std::cout << std::setw(4) << order << ' ';
+
+        // exponent of the strong coupling
+        std::uint32_t exp_as = order_params.at(4 * order + 0);
+        // exponent of the electromagnetic/electroweak coupling
+        std::uint32_t exp_al = order_params.at(4 * order + 1);
+        // exponent of the renormalization log
+        std::uint32_t exp_lr = order_params.at(4 * order + 2);
+        // exponent of the factorization log
+        std::uint32_t exp_lf = order_params.at(4 * order + 3);
+
+        std::cout << "O(as^" << exp_as << " a^" << exp_al << " lr^" << exp_lr << " lf^" << exp_lf
+            << ")\n";
+    }
+
+    // release memory
+    pineappl_grid_delete(grid);
+}