September 2017 Update

Task/Permutations/Stata/permutations-1.stata

@@ -0,0 +1 @@
+perm 4

Task/Permutations/Stata/permutations-2.stata

@@ -0,0 +1,49 @@
+program perm
+	local n=`1'
+	local r=1
+	forv i=1/`n' {
+		local r=`r'*`i'
+	}
+	clear
+	qui set obs `r'
+	forv i=1/`n' {
+		gen p`i'=0
+	}
+	mata: genperm()
+end
+
+mata
+void genperm() {
+	real scalar n, i, j, k, s, p
+	real rowvector u
+	st_view(a=., ., .)
+	n = cols(a)
+	u = 1..n
+	p = 1
+	do {
+		a[p++, .] = u
+		i = n
+		for (i = n; i > 1; i--) {
+			if (u[i-1] < u[i]) break
+		}
+		if (i > 1) {
+			j = i
+			k = n
+			while (j < k) {
+				s = u[j]
+				u[j] = u[k]
+				u[k] = s
+				j++
+				k--
+			}
+			
+			s = u[i-1]
+			j = i
+			for (j = i; u[j] < s; j++) {
+			}
+			u[i-1] = u[j]
+			u[j] = s
+		}
+	} while (i > 1)
+}
+end