From 9e81359999f98c99f297375a17cc35403f957d5f Mon Sep 17 00:00:00 2001
From: HOS <Hans.Olsson@3ds.com>
Date: Mon, 26 Oct 2026 13:58:18 +0100
Subject: [PATCH 1/2] Update determinant with better recommendations, and
 follow them. Closes #4687

---
 .../Electrical/Polyphase/Basic/MutualInductor.mo    |  2 +-
 .../QuasiStatic/Polyphase/Basic/MutualInductor.mo   |  2 +-
 Modelica/Math/package.mo                            | 13 ++++++-------
 3 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/Modelica/Electrical/Polyphase/Basic/MutualInductor.mo b/Modelica/Electrical/Polyphase/Basic/MutualInductor.mo
index b4a4ecb65d..c2b1c6a239 100644
--- a/Modelica/Electrical/Polyphase/Basic/MutualInductor.mo
+++ b/Modelica/Electrical/Polyphase/Basic/MutualInductor.mo
@@ -4,7 +4,7 @@ model MutualInductor "Linear mutual inductor"
   parameter Real epsilon=1e-9 "Relative accuracy tolerance of matrix symmetry";
   parameter SI.Inductance L[m, m] "Mutual inductance matrix";
 initial equation
-  if abs(Modelica.Math.Matrices.det(L)) < epsilon then
+  if Modelica.Math.Matrices.rcond(L) < epsilon then
     Modelica.Utilities.Streams.print("Warning: mutual inductance matrix singular!");
   end if;
 equation
diff --git a/Modelica/Electrical/QuasiStatic/Polyphase/Basic/MutualInductor.mo b/Modelica/Electrical/QuasiStatic/Polyphase/Basic/MutualInductor.mo
index 60f5aa27b8..47cd240a51 100644
--- a/Modelica/Electrical/QuasiStatic/Polyphase/Basic/MutualInductor.mo
+++ b/Modelica/Electrical/QuasiStatic/Polyphase/Basic/MutualInductor.mo
@@ -5,7 +5,7 @@ model MutualInductor "Linear mutual inductor"
   parameter Real epsilon=1e-9 "Relative accuracy tolerance of matrix symmetry";
   parameter SI.Inductance L[m, m] "Mutual inductance matrix";
 initial equation
-  if abs(Modelica.Math.Matrices.det(L)) < epsilon then
+  if Modelica.Math.Matrices.rcond(L) < epsilon then
     Modelica.Utilities.Streams.print("Warning: mutual inductance matrix singular!");
   end if;
 equation
diff --git a/Modelica/Math/package.mo b/Modelica/Math/package.mo
index 6a875a6082..8943ff27a6 100644
--- a/Modelica/Math/package.mo
+++ b/Modelica/Math/package.mo
@@ -2579,18 +2579,17 @@ result = Matrices.<strong>det</strong>(A);
 This function returns the determinant \"result\" of matrix A
 computed by a LU decomposition with row pivoting. For details about determinants, see
 <a href=\"http://en.wikipedia.org/wiki/Determinant\">http://en.wikipedia.org/wiki/Determinant</a>.
-Usually, this function should never be used, because
+Usually, this function should not be used, because
 there are nearly always better numerical algorithms
-as by computing the determinant. Examples:
+than computing the determinant. Examples:
 </p>
 
 <ul>
-<li> Use <a href=\"modelica://Modelica.Math.Matrices.rank\">Matrices.rank</a>
-     to compute whether det(A) = 0 (i.e., Matrices.rank(A) &lt; size(A,1)).</li>
-
 <li> Use <a href=\"modelica://Modelica.Math.Matrices.solve\">Matrices.solve</a>
-     to solve the linear equation A*x = b, instead of using determinants to
-     compute the solution.</li>
+     to solve the linear equation A*x = b.</li>
+
+<li> Use <a href=\"modelica://Modelica.Math.Matrices.rcond\"Matrices.rcond</a>(A)>=epsilon
+     to check that the system is well-conditioned and not singular.</li>
 </ul>
 
 <h4>See also</h4>

From 4d24b7e0f0f55cf19c65e0ee12cdb26f3d1c4c37 Mon Sep 17 00:00:00 2001
From: HOS <Hans.Olsson@3ds.com>
Date: Mon, 26 Oct 2026 14:03:49 +0100
Subject: [PATCH 2/2] FixSyntax

---
 Modelica/Math/package.mo | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Modelica/Math/package.mo b/Modelica/Math/package.mo
index 8943ff27a6..8794110767 100644
--- a/Modelica/Math/package.mo
+++ b/Modelica/Math/package.mo
@@ -2588,7 +2588,7 @@ than computing the determinant. Examples:
 <li> Use <a href=\"modelica://Modelica.Math.Matrices.solve\">Matrices.solve</a>
      to solve the linear equation A*x = b.</li>
 
-<li> Use <a href=\"modelica://Modelica.Math.Matrices.rcond\"Matrices.rcond</a>(A)>=epsilon
+<li> Use <a href=\"modelica://Modelica.Math.Matrices.rcond\">Matrices.rcond</a>(A)>=epsilon
      to check that the system is well-conditioned and not singular.</li>
 </ul>