Add Matrix columnSubtractScalar.

Author: markrogoyski

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New Features
 * Matrix `columnAddScalar`
 * Matrix `columnSubtract`
+* Matrix `columnSubtractScalar`
 
 ## v2.12.0 - 2025-10-17
 

README.md

@@ -503,12 +503,13 @@ $R = $A->rowSubtractScalar($mᵢ, $k);  // Subtract k from each item of row mᵢ
 // Column operations
 [$nᵢ, $nⱼ, $k] = [1, 2, 5];
 $R = $A->columnInterchange($nᵢ, $nⱼ);
-$R = $A->columnExclude($nᵢ);            // Exclude column $nᵢ
-$R = $A->columnMultiply($nᵢ, $k);       // Multiply column nᵢ by k
-$R = $A->columnAdd($nᵢ, $nⱼ, $k);       // Add k * column nᵢ to column nⱼ
-$R = $A->columnAddScalar($n, $k);       // Add k to each item in column nⱼ
-$R = $A->columnAddVector($nᵢ, $V);      // Add Vector V to column nᵢ
-$R = $A->columnSubtract($nᵢ, $nⱼ, $k);  // Subtract k * column nᵢ from row nⱼ
+$R = $A->columnExclude($nᵢ);             // Exclude column $nᵢ
+$R = $A->columnMultiply($nᵢ, $k);        // Multiply column nᵢ by k
+$R = $A->columnAdd($nᵢ, $nⱼ, $k);        // Add k * column nᵢ to column nⱼ
+$R = $A->columnAddScalar($n, $k);        // Add k to each item in column nⱼ
+$R = $A->columnAddVector($nᵢ, $V);       // Add Vector V to column nᵢ
+$R = $A->columnSubtract($nᵢ, $nⱼ, $k);   // Subtract k * column nᵢ from row nⱼ
+$R = $A->columnSubtractScalar($nᵢ, $k);  // Subtract k from each item of column nᵢ
 
 // Matrix augmentations - return a new Matrix
 $⟮A∣B⟯ = $A->augment($B);        // Augment on the right - standard augmentation

src/LinearAlgebra/NumericMatrix.php

@@ -2597,6 +2597,7 @@ public function rowSubtractScalar(int $mᵢ, float $k): NumericMatrix
      *  - columnAddScalar
      *  - columnAddVector
      *  - columnSubtract
+     *  - columnSubtractScalar
      **************************************************************************/
 
     /**
@@ -2746,6 +2747,35 @@ public function columnSubtract(int $nᵢ, int $nⱼ, float $k): NumericMatrix
         return MatrixFactory::createNumeric($R, $this->ε);
     }
 
+    /**
+     * Subtract a scalar k to each item of a column
+     *
+     * Each element of Column nᵢ will have k subtracted from it
+     *
+     * @param int   $nᵢ Column to subtract k from
+     * @param float $k scalar
+     *
+     * @return NumericMatrix
+     *
+     * @throws Exception\MatrixException if column to subtract does not exist
+     * @throws Exception\IncorrectTypeException
+     */
+    public function columnSubtractScalar(int $nᵢ, float $k): NumericMatrix
+    {
+        if ($nᵢ >= $this->n) {
+            throw new Exception\MatrixException('Column to subtract does not exist');
+        }
+
+        $m = $this->m;
+        $R = $this->A;
+
+        for ($i = 0; $i < $m; $i++) {
+            $R[$i][$nᵢ] -= $k;
+        }
+
+        return MatrixFactory::createNumeric($R, $this->ε);
+    }
+
     /**************************************************************************
      * MATRIX REDUCTIONS - Return a Matrix in a reduced form
      *  - ref (row echelon form)

tests/LinearAlgebra/Matrix/Numeric/MatrixColumnOperationsTest.php

@@ -615,4 +615,79 @@ public function testColumnSubtractExceptionColumnGreaterThanN()
         // When
         $A->columnSubtract(4, 5, 2);
     }
+
+    /**
+     * @test         columnSubtractScalar
+     * @dataProvider dataProviderForColumnSubtractScalar
+     * @param        array $A
+     * @param        int   $nᵢ
+     * @param        float $k
+     * @param        array $expectedMatrix
+     * @throws      \Exception
+     */
+    public function testColumnSubtractScalar(array $A, int $nᵢ, float $k, array $expectedMatrix)
+    {
+        // Given
+        $A = MatrixFactory::create($A);
+        $expectedMatrix = MatrixFactory::create($expectedMatrix);
+
+        // When
+        $R = $A->columnSubtractScalar($nᵢ, $k);
+
+        // Then
+        $this->assertEqualsWithDelta($expectedMatrix, $R, 0.00001);
+    }
+
+    /**
+     * @return array
+     */
+    public function dataProviderForColumnSubtractScalar(): array
+    {
+        return [
+            [
+                [
+                    [6, 7, 8],
+                    [7, 8, 9],
+                    [8, 9, 10],
+                ], 0, 5,
+                [
+                    [1, 7, 8],
+                    [2, 8, 9],
+                    [3, 9, 10],
+                ],
+            ],
+            [
+                [
+                    [6, 7, 8],
+                    [7, 8, 9],
+                    [8, 9, 10],
+                ], 0, 5.2,
+                [
+                    [0.8, 7, 8],
+                    [1.8, 8, 9],
+                    [2.8, 9, 10],
+                ],
+            ],
+        ];
+    }
+
+    /**
+     * @test   columnSubtractScalar column greater than n
+     * @throws \Exception
+     */
+    public function testColumnSubtractScalarExceptionColumnGreaterThanN()
+    {
+        // Given
+        $A = MatrixFactory::create([
+            [1, 2, 3],
+            [2, 3, 4],
+            [3, 4, 5],
+        ]);
+
+        // Then
+        $this->expectException(Exception\MatrixException::class);
+
+        // When
+        $A->columnSubtractScalar(4, 5);
+    }
 }