Early termination for single eigenpair calculation added

mrcdr · mrcdr · commit eb9800c93522 · 2025-12-29T19:35:40.000+09:00
diff --git a/include/lambda_lanczos/lambda_lanczos.hpp b/include/lambda_lanczos/lambda_lanczos.hpp
@@ -346,6 +346,11 @@ class LambdaLanczos {
       if (nothing_added) {
         break;
       }
+
+      if (this->num_eigs == 1) {
+        // If only one eigenpair is required, iteration can be stopped
+        break;
+      }
     }
 
     const auto& eigenpairs = ep_manager.getEigenpairs();
diff --git a/test/lambda_lanczos_test.cpp b/test/lambda_lanczos_test.cpp
@@ -157,6 +157,7 @@ TEST(DIAGONALIZE_TEST, SIMPLE_MATRIX) {
   for (size_t i = 0; i < n; ++i) {
     EXPECT_NEAR(correct_eigvec[i], eigvec[i], std::abs(correct_eigvalue * engine.eps * 10));
   }
+  EXPECT_EQ(engine.getIterationCounts().size(), 1);
 }
 
 TEST(DIAGONALIZE_TEST, SIMPLE_MATRIX_FLOAT) {

Original file line number	Diff line number	Diff line change
`@@ -346,6 +346,11 @@ class LambdaLanczos {`
`346`	`346`	`if (nothing_added) {`
`347`	`347`	`break;`
`348`	`348`	`}`
	`349`	`+`
	`350`	`+ if (this->num_eigs == 1) {`
	`351`	`+ // If only one eigenpair is required, iteration can be stopped`
	`352`	`+ break;`
	`353`	`+ }`
`349`	`354`	`}`
`350`	`355`
`351`	`356`	`const auto& eigenpairs = ep_manager.getEigenpairs();`
Original file line number	Diff line number	Diff line change
`@@ -157,6 +157,7 @@ TEST(DIAGONALIZE_TEST, SIMPLE_MATRIX) {`
`157`	`157`	`for (size_t i = 0; i < n; ++i) {`
`158`	`158`	`EXPECT_NEAR(correct_eigvec[i], eigvec[i], std::abs(correct_eigvalue * engine.eps * 10));`
`159`	`159`	`}`
	`160`	`+ EXPECT_EQ(engine.getIterationCounts().size(), 1);`
`160`	`161`	`}`
`161`	`162`
`162`	`163`	`TEST(DIAGONALIZE_TEST, SIMPLE_MATRIX_FLOAT) {`