From e94d21ee3a2d7d053899d490b115ba763d0a1bc2 Mon Sep 17 00:00:00 2001
From: rodri <rgl@antares-labs.eu>
Date: Wed, 20 Dec 2023 11:27:36 +0000
Subject: [PATCH] libgeometry: add matrix minor and cofactor functions

---
 sys/include/geometry.h       |  4 ++++
 sys/man/2/geometry           | 26 ++++++++++++++++++++++++-
 sys/src/libgeometry/matrix.c | 37 ++++++++++++++++++++++++++++++++++++
 3 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/sys/include/geometry.h b/sys/include/geometry.h
index 401ed2ae7..31c2ebde6 100644
--- a/sys/include/geometry.h
+++ b/sys/include/geometry.h
@@ -84,6 +84,8 @@ void smulm(Matrix, double);
 void transposem(Matrix);
 double detm(Matrix);
 double tracem(Matrix);
+double minorm(Matrix, int, int);
+double cofactorm(Matrix, int, int);
 void adjm(Matrix);
 void invm(Matrix);
 Point2 xform(Point2, Matrix);
@@ -97,6 +99,8 @@ void smulm3(Matrix3, double);
 void transposem3(Matrix3);
 double detm3(Matrix3);
 double tracem3(Matrix3);
+double minorm3(Matrix3, int, int);
+double cofactorm3(Matrix3, int, int);
 void adjm3(Matrix3);
 void invm3(Matrix3);
 Point3 xform3(Point3, Matrix3);
diff --git a/sys/man/2/geometry b/sys/man/2/geometry
index 9eeb57c53..8f8de54aa 100644
--- a/sys/man/2/geometry
+++ b/sys/man/2/geometry
@@ -1,6 +1,6 @@
 .TH GEOMETRY 2
 .SH NAME
-Flerp, fclamp, Pt2, Vec2, addpt2, subpt2, mulpt2, divpt2, lerp2, dotvec2, vec2len, normvec2, edgeptcmp, ptinpoly, Pt3, Vec3, addpt3, subpt3, mulpt3, divpt3, lerp3, dotvec3, crossvec3, vec3len, normvec3, identity, addm, subm, mulm, smulm, transposem, detm, tracem, adjm, invm, xform, identity3, addm3, subm3, mulm3, smulm3, transposem3, detm3, tracem3, adjm3, invm3, xform3, Quat, Quatvec, addq, subq, mulq, smulq, sdivq, dotq, invq, qlen, normq, slerp, qrotate, rframexform, rframexform3, invrframexform, invrframexform3, centroid, barycoords, centroid3, vfmt, Vfmt, GEOMfmtinstall \- computational geometry library
+Flerp, fclamp, Pt2, Vec2, addpt2, subpt2, mulpt2, divpt2, lerp2, dotvec2, vec2len, normvec2, edgeptcmp, ptinpoly, Pt3, Vec3, addpt3, subpt3, mulpt3, divpt3, lerp3, dotvec3, crossvec3, vec3len, normvec3, identity, addm, subm, mulm, smulm, transposem, detm, tracem, minorm, cofactorm, adjm, invm, xform, identity3, addm3, subm3, mulm3, smulm3, transposem3, detm3, tracem3, minorm3, cofactorm3, adjm3, invm3, xform3, Quat, Quatvec, addq, subq, mulq, smulq, sdivq, dotq, invq, qlen, normq, slerp, qrotate, rframexform, rframexform3, invrframexform, invrframexform3, centroid, barycoords, centroid3, vfmt, Vfmt, GEOMfmtinstall \- computational geometry library
 .SH SYNOPSIS
 .de PB
 .PP
@@ -95,6 +95,8 @@ void smulm(Matrix m, double s);
 void transposem(Matrix m);
 double detm(Matrix m);
 double tracem(Matrix m);
+double minorm(Matrix m, int row, int col);
+double cofactorm(Matrix m, int row, int col);
 void adjm(Matrix m);
 void invm(Matrix m);
 Point2 xform(Point2 p, Matrix m);
@@ -108,6 +110,8 @@ void smulm3(Matrix3 m, double s);
 void transposem3(Matrix3 m);
 double detm3(Matrix3 m);
 double tracem3(Matrix3 m);
+double minorm3(Matrix3 m, int row, int col);
+double cofactorm3(Matrix3 m, int row, int col);
 void adjm3(Matrix3 m);
 void invm3(Matrix3 m);
 Point3 xform3(Point3 p, Matrix3 m);
@@ -386,6 +390,16 @@ Computes the trace of
 .I m
 and returns the result.
 .TP
+.B minorm(\fIm\fP,\fIrow\fP,\fIcol\fP)
+Computes the minor of
+.I m
+and returns the result.
+.TP
+.B cofactorm(\fIm\fP,\fIrow\fP,\fIcol\fP)
+Computes the cofactor of
+.I m
+and returns the result.
+.TP
 .B adjm(\fIm\fP)
 Transforms the matrix
 .I m
@@ -454,6 +468,16 @@ Computes the trace of
 .I m
 and returns the result.
 .TP
+.B minorm3(\fIm\fP,\fIrow\fP,\fIcol\fP)
+Computes the minor of
+.I m
+and returns the result.
+.TP
+.B cofactorm3(\fIm\fP,\fIrow\fP,\fIcol\fP)
+Computes the cofactor of
+.I m
+and returns the result.
+.TP
 .B adjm3(\fIm\fP)
 Transforms the matrix
 .I m
diff --git a/sys/src/libgeometry/matrix.c b/sys/src/libgeometry/matrix.c
index d640403a7..5eebbb18a 100644
--- a/sys/src/libgeometry/matrix.c
+++ b/sys/src/libgeometry/matrix.c
@@ -84,6 +84,24 @@ tracem(Matrix m)
 	return m[0][0] + m[1][1] + m[2][2];
 }
 
+double
+minorm(Matrix m, int row, int col)
+{
+	int i, j;
+	double subm[2][2];
+
+	for(i = 0; i < 3-1; i++)
+		for(j = 0; j < 3-1; j++)
+			subm[i][j] = m[i < row? i: i+1][j < col? j: j+1];
+	return subm[0][0]*subm[1][1] - subm[0][1]*subm[1][0];
+}
+
+double
+cofactorm(Matrix m, int row, int col)
+{
+	return minorm(m, row, col)*((row+col)&1 == 0? 1: -1);
+}
+
 void
 adjm(Matrix m)
 {
@@ -238,6 +256,25 @@ tracem3(Matrix3 m)
 	return m[0][0] + m[1][1] + m[2][2] + m[3][3];
 }
 
+double
+minorm3(Matrix3 m, int row, int col)
+{
+	int i, j;
+	Matrix subm;
+
+	memset(subm, 0, sizeof subm);
+	for(i = 0; i < 4-1; i++)
+		for(j = 0; j < 4-1; j++)
+			subm[i][j] = m[i < row? i: i+1][j < col? j: j+1];
+	return detm(subm);
+}
+
+double
+cofactorm3(Matrix3 m, int row, int col)
+{
+	return minorm3(m, row, col)*((row+col)&1 == 0? 1: -1);
+}
+
 void
 adjm3(Matrix3 m)
 {