From b80384c71577cc089854248120c157d1d78c7e3d Mon Sep 17 00:00:00 2001
From: user1823 <92206575+user1823@users.noreply.github.com>
Date: Sat, 25 Jan 2025 15:45:49 +0530
Subject: [PATCH] More accurate sorting by R (#3747)

* Match calc of relative overdueness in SM2 and FSRS

* Fix calculation of FSRS relative overdueness

* Improve readability by avoiding double negative

* Move comment line
---
 rslib/src/storage/card/mod.rs | 3 ++-
 rslib/src/storage/sqlite.rs   | 4 +++-
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/rslib/src/storage/card/mod.rs b/rslib/src/storage/card/mod.rs
index 93c689292..4cc7fd626 100644
--- a/rslib/src/storage/card/mod.rs
+++ b/rslib/src/storage/card/mod.rs
@@ -775,7 +775,8 @@ impl fmt::Display for ReviewOrderSubclause {
             ReviewOrderSubclause::DifficultyDescending => "extract_fsrs_variable(data, 'd') desc",
             ReviewOrderSubclause::RetrievabilitySm2 { today, order } => {
                 temp_string = format!(
-                    "ivl / cast({today}-due+0.001 as real) {order}",
+                    // - (elapsed days+0.001)/(scheduled interval)
+                    "-(1 + cast({today}-due+0.001 as real)/ivl) {order}",
                     today = today
                 );
                 &temp_string
diff --git a/rslib/src/storage/sqlite.rs b/rslib/src/storage/sqlite.rs
index f0341f699..0775ac7b4 100644
--- a/rslib/src/storage/sqlite.rs
+++ b/rslib/src/storage/sqlite.rs
@@ -388,7 +388,9 @@ fn add_extract_fsrs_relative_retrievability(db: &Connection) -> rusqlite::Result
                 .max(0.0001);
 
             Ok(Some(
-                -(1. / current_retrievability - 1.) / (1. / desired_retrievability - 1.),
+                // power should be the reciprocal of the value of DECAY in FSRS-rs, which is
+                // currently -0.5
+                -(current_retrievability.powi(-2) - 1.) / (desired_retrievability.powi(-2) - 1.),
             ))
         },
     )