added Gauss-Jordan

gallery/example3.typ

@@ -0,0 +1,27 @@
+#import "/src/lib.typ": *
+
+#let A = mat.mat(
+  (3, -3, -1, 2, -9),
+  (1, -1, 2, -1, -6),
+  (1, -1, 1, 1, -6),
+  (-1, 1, -1, -2, 7)
+)
+
+#let b = vec.vec(13, -6, 1, -3)
+
+#let A2 = mat.mul-row(A, 2, 3)
+#let A3 = mat.div-row(A, 1, 2)
+#let A4 = mat.add-row(A, 2, 3, f: 2)
+
+$
+  A = #mat.display(A) quad b = #vec.display(b)\
+  A_2 = #mat.display(A2)\
+  A_3 = #mat.display(A3)\
+  A_4 = #mat.display(A4)\
+$
+
+#let E = gauss.echelon(A)
+
+$
+  E = #mat.display(E)
+$