Make PPCG tests C++11 compatible

Author: cheerly-pku

source/source_hsolver/diago_ppcg.h

@@ -11,6 +11,7 @@
 #include <stdexcept>
 #include <numeric>
 #include <complex>
+#include <type_traits>
 
 namespace hsolver {
 

source/source_hsolver/test/diago_ppcg_test.cpp

@@ -2322,7 +2322,9 @@ TEST_F(DiagoPPCGBenchmarkTest, DISABLED_FullBenchmark)
         std::vector<T> H;
         std::vector<Real> prec;
         make_random_hamilt(c.n, c.sparsity, H, prec);
-        auto [avg_iter, wall] = run_ppcg(c.n, c.nband, H, prec);
+        const std::pair<double, double> result = run_ppcg(c.n, c.nband, H, prec);
+        const double avg_iter = result.first;
+        const double wall = result.second;
         printf(" %5d   %3d     %2d%%       %6.1f      %7.4f\n",
                c.n, c.nband, c.sparsity, avg_iter, wall);
     }
@@ -2336,7 +2338,9 @@ TEST_F(DiagoPPCGBenchmarkTest, QuickBenchmark)
     std::vector<T> H;
     std::vector<Real> prec;
     make_random_hamilt(80, 60, H, prec);
-    auto [avg_iter, wall] = run_ppcg(80, 8, H, prec);
+    const std::pair<double, double> result = run_ppcg(80, 8, H, prec);
+    const double avg_iter = result.first;
+    const double wall = result.second;
     std::cout << "[PPCG QuickBench] n=80 nband=8 sparsity=60%"
               << " avg_iter=" << avg_iter << " wall=" << wall << "s\n";
     EXPECT_LE(avg_iter, 500.0) << "PPCG did not converge within 500 iters";