From 0163b4a48e5a34ace868484ee59139d83d6fd758 Mon Sep 17 00:00:00 2001
From: Ezrnest <1403718476@qq.com>
Date: Fri, 20 Feb 2026 16:58:58 +0800
Subject: [PATCH] Fix Matrix.fromColumns indexing and add regression tests

---
 .../github/ezrnest/mathsymk/linear/Matrix.kt  |  4 +--
 src/test/kotlin/linear/MatrixTest.kt          | 32 +++++++++++++++++++
 2 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/src/main/kotlin/io/github/ezrnest/mathsymk/linear/Matrix.kt b/src/main/kotlin/io/github/ezrnest/mathsymk/linear/Matrix.kt
index 0ba5ac0..f2e44b1 100644
--- a/src/main/kotlin/io/github/ezrnest/mathsymk/linear/Matrix.kt
+++ b/src/main/kotlin/io/github/ezrnest/mathsymk/linear/Matrix.kt
@@ -252,7 +252,7 @@ interface Matrix<T> : GenTuple<T> {
             val row = columns.first().size
             val column = columns.size
             require(columns.all { it.size == row })
-            return Matrix(row, column) { i, j -> columns[i][j] }
+            return Matrix(row, column) { i, j -> columns[j][i] }
         }
 
         /**
@@ -1564,4 +1564,4 @@ internal class MatOverFieldImpl<T>(override val model: Field<T>, row: Int, colum
 //        require(ps.all { it in this })
 //        return MatrixImpl.product(ps, model)
 //    }
-//}
\ No newline at end of file
+//}
diff --git a/src/test/kotlin/linear/MatrixTest.kt b/src/test/kotlin/linear/MatrixTest.kt
index 0bf29d0..73fd784 100644
--- a/src/test/kotlin/linear/MatrixTest.kt
+++ b/src/test/kotlin/linear/MatrixTest.kt
@@ -17,6 +17,38 @@ import kotlin.test.assertEquals
 import kotlin.test.assertTrue
 
 class MatrixTest {
+
+    @Test
+    fun fromColumnsKeepsColumnMajorPlacement() {
+        val columns = List(3) { col ->
+            Vector(3) { row -> 10 * col + row }
+        }
+        val matrix = Matrix.fromColumns(columns)
+
+        for (row in 0 until matrix.row) {
+            for (col in 0 until matrix.column) {
+                assertEquals(columns[col][row], matrix[row, col])
+            }
+        }
+    }
+
+    @Test
+    fun fromColumnsKeepsColumnMajorPlacementForRectangularMatrix() {
+        val columns = List(3) { col ->
+            Vector(2) { row -> 10 * col + row }
+        }
+        val matrix = Matrix.fromColumns(columns)
+
+        assertEquals(2, matrix.row)
+        assertEquals(3, matrix.column)
+        for (row in 0 until matrix.row) {
+            for (col in 0 until matrix.column) {
+                assertEquals(columns[col][row], matrix[row, col])
+            }
+        }
+    }
+
+
     val Z = Models.ints()
     val Zmod7 = Models.intModP(7)
     val Zmod97 = Models.intModP(97)