fix(pinv): write a typescript definition and test (#2804)

* fix(pinv): write a typescript definition

* fix(pinv): write a typescript test

* fix(pinv): format types/index.ts

* fix(pinv): format types/index.ts

* fix(pinv): format types/index.d.ts

* fix(pinv): format types/index.ts

Co-authored-by: Jos de Jong <wjosdejong@gmail.com>

types/index.d.ts

@@ -1898,6 +1898,13 @@ declare namespace math {
       // eslint-disable-next-line @typescript-eslint/no-explicit-any
     ): any
 
+    /**
+     * Calculate the Moore–Penrose inverse of a matrix.
+     * @param x Matrix to be inversed
+     * @return The inverse of `x`.
+     */
+    pinv<T extends MathType>(x: T): T
+
     /**
      * Create an array from a range. By default, the range end is excluded.
      * This can be customized by providing an extra parameter includeEnd.

types/index.ts

@@ -1293,6 +1293,37 @@ Matrices examples
       )
     )
   }
+
+  // Moore–Penrose inverse
+  {
+    assert.ok(
+      math.deepEqual(
+        math.pinv([
+          [1, 2],
+          [3, 4],
+        ]),
+        [
+          [-2, 1],
+          [1.5, -0.5],
+        ]
+      )
+    )
+    assert.ok(
+      math.deepEqual(
+        math.pinv(
+          math.matrix([
+            [1, 2],
+            [3, 4],
+          ])
+        ),
+        math.matrix([
+          [-2, 1],
+          [1.5, -0.5],
+        ])
+      )
+    )
+    assert.ok(math.deepEqual(math.pinv(4), 0.25))
+  }
 }
 
 /*