Added inverse and unary minus of Matrix.

Author: phlegmaticprogrammer

README.md

@@ -430,6 +430,8 @@ A ′∖ .eye(3): 3x3-matrix:
 ⎝-0.01953124999999994  -0.08984374999999999  -0.19531249999999994⎠
 ```
 
+The inverse of `A` can more concisely also be obtained via `A.inverse!`.
+
 ## Matrix Decompositions
 
 The following matrix decompositions are currently supported:

Sources/LANumerics/LANumeric.swift

@@ -440,7 +440,7 @@ public extension LANumeric {
             return nil
         }
     }
-
+    
 }
 
 infix operator ′* : MultiplicationPrecedence
@@ -510,6 +510,10 @@ public extension Matrix where Element : LANumeric {
         return result
     }
 
+    static prefix func -(matrix : Matrix) -> Matrix {
+        return -1 * matrix
+    }
+    
     static func += (left : inout Matrix, right : Matrix) {
         left.accumulate(1, 1, right)
     }
@@ -625,7 +629,7 @@ public extension Matrix where Element : LANumeric {
         guard let result = Element.schurDecomposition(&A) else { return nil }
         return (eigenValues: result.eigenValues, schurForm: A, schurVectors: result.schurVectors)
     }
-
+    
     static func ∖ (lhs : Matrix, rhs : Matrix) -> Matrix {
         return lhs.solveLeastSquares(rhs)!
     }
@@ -641,6 +645,11 @@ public extension Matrix where Element : LANumeric {
     static func ′∖ (lhs : Matrix, rhs : Vector<Element>) -> Vector<Element> {
         return lhs.solveLeastSquares(transpose: .adjoint, rhs)!
     }
+    
+    var inverse : Matrix? {
+        guard rows == columns else { return nil }
+        return self.solveLeastSquares(.eye(rows))
+    }
 
 }