From f33e3b579d685a570cd7edf1b9a10944c379c491 Mon Sep 17 00:00:00 2001
From: fis <jm.yuan@outlook.com>
Date: Thu, 28 May 2020 18:19:13 +0800
Subject: [PATCH] Fix loading old model.

---
 src/learner.cc | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/src/learner.cc b/src/learner.cc
index de9620c9a8b2..1b92d1db77b5 100644
--- a/src/learner.cc
+++ b/src/learner.cc
@@ -694,15 +694,24 @@ class LearnerIO : public LearnerConfiguration {
       warn_old_model = false;
     }
 
-    if (mparam_.major_version >= 1) {
-      learner_model_param_ = LearnerModelParam(mparam_,
-                                               obj_->ProbToMargin(mparam_.base_score));
-    } else {
+    if (mparam_.major_version < 1) {
       // Before 1.0.0, base_score is saved as a transformed value, and there's no version
       // attribute in the saved model.
-      learner_model_param_ = LearnerModelParam(mparam_, mparam_.base_score);
+      std::string multi{"multi:"};
+      if (!std::equal(tparam_.objective.cbegin(), tparam_.objective.cend(),
+                      multi.begin())) {
+        HostDeviceVector<float> t;
+        t.HostVector().resize(1);
+        t.HostVector().at(0) = mparam_.base_score;
+        this->obj_->PredTransform(&t);
+        auto base_score = t.HostVector().at(0);
+        mparam_.base_score = base_score;
+      }
       warn_old_model = true;
     }
+
+    learner_model_param_ =
+        LearnerModelParam(mparam_, obj_->ProbToMargin(mparam_.base_score));
     if (attributes_.find("objective") != attributes_.cend()) {
       auto obj_str = attributes_.at("objective");
       auto j_obj = Json::Load({obj_str.c_str(), obj_str.size()});