fix #207 in cholesky decomposition

A precedence error in the binary block of #inject:into was causing cholesky decomposition to fail for matrices of size more than 3.
It has been corrected by adding parenthesis in the block.
New tests with matrix size more than 3 has also been added.

Author: rakki-18

src/Math-Matrix/PMMatrix.class.st

@@ -366,15 +366,20 @@ PMMatrix >> choleskyDecomposition [
 
 					diagonalValue := ((self at: j at: j) - rowSum) sqrt.
 
+
 					upperTriangular at: j at: j put: diagonalValue ]
 				ifFalse: [
-					partialSum := (1 to: j - 1) inject: 0 into: [ :sum :k |
-						sum + (upperTriangular at: k at: i) * (upperTriangular at: k at: j) ].
 
+					partialSum := (1 to: j - 1) inject: 0 into: [ :sum :k |
+							sum + ((upperTriangular at: k at: i) * (upperTriangular at: k at: j)).
+						].
+					
 					factor := upperTriangular at: j at: j.
 					nonDiagonalValue := ((self at: j at: i) - partialSum) / factor.
 
-					upperTriangular at: j at: i put: nonDiagonalValue ] ] ].
+					upperTriangular at: j at: i put: nonDiagonalValue.
+					
+				] ] ].
 
 	^ upperTriangular
 ]

src/Math-Tests-Matrix/PMMatrixTest.class.st

@@ -76,16 +76,20 @@ PMMatrixTest >> testCholeskyDecomposition [
 	| matrix upperTriangular expected |
 
 	matrix := PMMatrix rows: #(
-		(4 12 -16)
-		(12 37 -43)
-		(-16 -43 98)).
+		(4 20 8 2 18)
+		(20 116 80 18 126)
+		(8 80 117 32 135)
+		(2 18 32 73 109)
+		(18 126 135 109 272)).
 
 	upperTriangular := matrix choleskyDecomposition.
 
 	expected := PMMatrix rows: #(
-		(2 6 -8)
-		(0 1 5)
-		(0 0 3)).
+		(2 10 4 1 9)
+		(0 4 10 2 9)
+		(0 0 1 8 9)
+		(0 0 0 2 5)
+		(0 0 0 0 2)).
 
 	self assert: upperTriangular equals: expected.
 ]