From 2ec87b2287fcb6f20d7f617cfabd04bc00e218f1 Mon Sep 17 00:00:00 2001
From: Justin Lin <caterpillar@openhome.cc>
Date: Wed, 26 Feb 2020 09:36:55 +0800
Subject: [PATCH] add m_determinant

---
 .../_impl/_m_determinant_impl.scad            | 20 +++++++++++++++++++
 src/experimental/m_determinant.scad           |  3 +++
 2 files changed, 23 insertions(+)
 create mode 100644 src/experimental/_impl/_m_determinant_impl.scad
 create mode 100644 src/experimental/m_determinant.scad

diff --git a/src/experimental/_impl/_m_determinant_impl.scad b/src/experimental/_impl/_m_determinant_impl.scad
new file mode 100644
index 00000000..f838921b
--- /dev/null
+++ b/src/experimental/_impl/_m_determinant_impl.scad
@@ -0,0 +1,20 @@
+use <util/slice.scad>;
+
+function _m_determinant_sum(lt, leng, i = 0) =
+    i == leng ? 0 : (lt[i] + _m_determinant_sum(lt, leng, i + 1));
+
+function _m_determinant_sub(matrix, leng, fc) = 
+    let(
+        init_sub_m = [for(i = [1:leng - 1]) matrix[i]],
+        sub_m = [for(i = [0:len(init_sub_m) - 1]) 
+            concat(slice(init_sub_m[i], 0, fc), slice(init_sub_m[i], fc + 1))
+        ],
+        sgn = pow(-1, fc % 2)
+    )
+    sgn * matrix[0][fc] * _m_determinant(sub_m);
+
+function _m_determinant(matrix) = 
+    let(leng = len(matrix))
+    leng == 2 ? matrix[0][0] * matrix[1][1] - matrix[1][0] * matrix[0][1] :
+        let(indices = [for(i = [0:leng - 1]) i])
+        _m_determinant_sum([for(fc = indices) _m_determinant_sub(matrix, leng, fc)], leng);
\ No newline at end of file
diff --git a/src/experimental/m_determinant.scad b/src/experimental/m_determinant.scad
new file mode 100644
index 00000000..b131dc55
--- /dev/null
+++ b/src/experimental/m_determinant.scad
@@ -0,0 +1,3 @@
+use <experimental/_impl/_m_determinant_impl.scad>;
+
+function m_determinant(matrix) = _m_determinant(matrix);
\ No newline at end of file