EulerPhi and PowerMod.

corywalker · Nov 2, 2017 · 7774064 · 7774064
1 parent 219c991
commit 7774064
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Showing 3 changed files with 32 additions and 2 deletions.
diff --git a/expreduce/builtin_numbertheory.go b/expreduce/builtin_numbertheory.go
@@ -149,5 +149,7 @@ func GetNumberTheoryDefinitions() (defs []Definition) {
 	defs = append(defs, Definition{Name: "FactorInteger"})
 	defs = append(defs, Definition{Name: "FractionalPart"})
 	defs = append(defs, Definition{Name: "IntegerPart"})
+	defs = append(defs, Definition{Name: "PowerMod"})
+	defs = append(defs, Definition{Name: "EulerPhi"})
 	return
 }
diff --git a/expreduce/resources.go b/expreduce/resources.go
diff --git a/expreduce/resources/numbertheory.m b/expreduce/resources/numbertheory.m
@@ -224,3 +224,31 @@
         ESameTest[1,IntegerPart[1]],
     ]
 };
+
+PowerMod::usage = "`PowerMod[x, y, m]` computes `Mod[x^y, m]`";
+(*TODO: use efficient version of this function.*)
+PowerMod[x_, y_, m_] := Mod[x^y, m];
+Attributes[PowerMod] = {Listable, Protected, ReadProtected};
+Tests`PowerMod = {
+    ESimpleExamples[
+        ESameTest[6,PowerMod[5, 9999, 7]],
+    ]
+};
+
+EulerPhi::usage = "`EulerPhi[n]` computes Euler's totient function for `n`";
+Attributes[EulerPhi] = {Listable, Protected, ReadProtected};
+EulerPhi[0] := 0;
+EulerPhi[n_Integer?Positive] := 
+ If[n === 1, 1,
+ n*Product[1 - 1/p[[1]], {p, FactorInteger[n]}]];
+EulerPhi[n_Integer?Negative] := EulerPhi[-n];
+Tests`EulerPhi = {
+    ESimpleExamples[
+        ESameTest[42,EulerPhi[98]],
+        ESameTest[0,EulerPhi[0]],
+        ESameTest[42,EulerPhi[-98]],
+    ], ETests[
+        ESameTest[1,EulerPhi[1]],
+        ESameTest[1,EulerPhi[-1]],
+    ]
+};