June 2018 Update

Task/Zig-zag-matrix/Stata/zig-zag-matrix-1.stata

@@ -0,0 +1,22 @@
+function zigzag1(n) {
+	j = 0::n-1
+	u = J(1, n, (-1, 1))
+	v = (j:*(2:*j:+3))
+	v = rowshape((v,v:+1), 1)
+	a = J(n, n, .)
+	for (i=1; i<=n; i++) {
+		a[i, .] = v[j:+i]
+		v = v+u
+	}
+	return(a)
+}
+
+zigzag1(5)
+        1    2    3    4    5
+    +--------------------------+
+  1 |   0    1    5    6   14  |
+  2 |   2    4    7   13   16  |
+  3 |   3    8   12   17   25  |
+  4 |   9   11   18   24   31  |
+  5 |  10   19   23   32   40  |
+    +--------------------------+

Task/Zig-zag-matrix/Stata/zig-zag-matrix-2.stata

@@ -0,0 +1,18 @@
+function zigzag2(n) {
+	a = zigzag1(n)
+	v = (1..n-1):^2
+	for (i=1; i<n; i++) {
+		a[n-i+1, i+1..n] = a[n-i+1, i+1..n] - v[1..n-i]
+	}
+	return(a)
+}
+
+zigzag2(5)
+        1    2    3    4    5
+    +--------------------------+
+  1 |   0    1    5    6   14  |
+  2 |   2    4    7   13   15  |
+  3 |   3    8   12   16   21  |
+  4 |   9   11   17   20   22  |
+  5 |  10   18   19   23   24  |
+    +--------------------------+

Task/Zig-zag-matrix/Stata/zig-zag-matrix-3.stata

@@ -0,0 +1,10 @@
+zigzag1(5)-zigzag2(5)
+[symmetric]
+        1    2    3    4    5
+    +--------------------------+
+  1 |   0                      |
+  2 |   0    0                 |
+  3 |   0    0    0            |
+  4 |   0    0    1    4       |
+  5 |   0    1    4    9   16  |
+    +--------------------------+