June 2018 Update

Task/Matrix-arithmetic/Stata/matrix-arithmetic-1.stata

@@ -0,0 +1,28 @@
+real vector range1(real scalar n, real scalar i) {
+	if (i < 1 | i > n) {
+		return(1::n)
+	} else if (i == 1) {
+		return(2::n)
+	} else if (i == n) {
+		return(1::n-1)
+	} else {
+		return(1::i-1\i+1::n)
+	}
+}
+
+real matrix submat(real matrix a, real scalar i, real scalar j) {
+	return(a[range1(rows(a), i), range1(cols(a), j)])
+}
+
+real scalar sumrec(real matrix a, real scalar x) {
+	real scalar n, s, p
+	n = rows(a)
+	if (n==1) return(a[1,1])
+	s = 0
+	p = 1
+	for (i=1; i<=n; i++) {
+		s = s+p*a[i,1]*sumrec(submat(a, i, 1), x)
+		p = p*x
+	}
+	return(s)
+}

Task/Matrix-arithmetic/Stata/matrix-arithmetic-2.stata

@@ -0,0 +1,19 @@
+: a=1,1,1,0\1,1,0,1\1,0,1,1\0,1,1,1
+: a
+[symmetric]
+       1   2   3   4
+    +-----------------+
+  1 |  1              |
+  2 |  1   1          |
+  3 |  1   0   1      |
+  4 |  0   1   1   1  |
+    +-----------------+
+
+: det(a)
+  -3
+
+: sumrec(a,-1)
+  -3
+
+: sumrec(a,1)
+  9