From ce08ba94394d00bfb2312aecea53b0b114a6f2a9 Mon Sep 17 00:00:00 2001
From: Trevor Blackwell <tlb@tlb.org>
Date: Sat, 13 Aug 2022 12:01:01 -0700
Subject: [PATCH 1/2] Avoid alphaStar = -inf when du contains a zero

When du(i) = 0 and it's approaching a lower bound, FindAlpha can return -inf. It should only return values in [0,1].
The added check fixes it
---
 include/cppoptlib/solver/lbfgsb.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/cppoptlib/solver/lbfgsb.h b/include/cppoptlib/solver/lbfgsb.h
index c0253f7..b46cc67 100644
--- a/include/cppoptlib/solver/lbfgsb.h
+++ b/include/cppoptlib/solver/lbfgsb.h
@@ -242,13 +242,14 @@ class Lbfgsb : public Solver<function_t> {
             alphastar,
             (upper_bound_(free_variables.at(i)) - x_cp(free_variables.at(i))) /
                 du(i));
-      } else {
+      } else if (du(i) < 0) {
         alphastar = std::min<scalar_t>(
             alphastar,
             (lower_bound_(free_variables.at(i)) - x_cp(free_variables.at(i))) /
                 du(i));
       }
     }
+    assert(alphastar >= 0);
     return alphastar;
   }
 

From dfd85a4fc3501e010d84ba39c5745a235d6e544a Mon Sep 17 00:00:00 2001
From: Trevor Blackwell <tlb@tlb.org>
Date: Sat, 13 Aug 2022 12:13:49 -0700
Subject: [PATCH 2/2] Fix alphaStar=-inf

---
 include/cppoptlib/solver/lbfgsb.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/cppoptlib/solver/lbfgsb.h b/include/cppoptlib/solver/lbfgsb.h
index c0253f7..963a9de 100644
--- a/include/cppoptlib/solver/lbfgsb.h
+++ b/include/cppoptlib/solver/lbfgsb.h
@@ -242,13 +242,15 @@ class Lbfgsb : public Solver<function_t> {
             alphastar,
             (upper_bound_(free_variables.at(i)) - x_cp(free_variables.at(i))) /
                 du(i));
-      } else {
+      }
+      else if (du(i) < 0) {
         alphastar = std::min<scalar_t>(
             alphastar,
             (lower_bound_(free_variables.at(i)) - x_cp(free_variables.at(i))) /
                 du(i));
       }
     }
+    assert(alphastar >= 0);
     return alphastar;
   }