Golden ratio

ca.h

@@ -317,6 +317,8 @@ void ca_pi(ca_t res, ca_ctx_t ctx);
 void ca_pi_i(ca_t res, ca_ctx_t ctx);
 void ca_euler(ca_t res, ca_ctx_t ctx);
 
+void ca_phi(ca_t res, ca_ctx_t ctx);
+
 void ca_unknown(ca_t x, ca_ctx_t ctx);
 
 void ca_undefined(ca_t x, ca_ctx_t ctx);

ca/phi.c

@@ -0,0 +1,25 @@
+/*
+    Copyright (C) 2020 Fredrik Johansson
+    Copyright (C) 2022 Raoul Bourquin
+
+    This file is part of Calcium.
+
+    Calcium is free software: you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License (LGPL) as published
+    by the Free Software Foundation; either version 2.1 of the License, or
+    (at your option) any later version.  See <http://www.gnu.org/licenses/>.
+*/
+
+#include "ca.h"
+
+void
+ca_phi(ca_t res, ca_ctx_t ctx)
+{
+    qqbar_t phi;
+    qqbar_init(phi);
+    qqbar_phi(phi);
+
+    ca_set_qqbar(res, phi, ctx);
+
+    qqbar_clear(phi);
+}

ca/set_fexpr.c

@@ -75,9 +75,7 @@ _ca_set_fexpr(ca_t res, fexpr_vec_t inputs, ca_vec_t outputs, const fexpr_t expr
                 ca_euler(res, ctx);
                 return 1;
             case FEXPR_GoldenRatio:
-                ca_sqrt_ui(res, 5, ctx);
-                ca_add_ui(res, res, 1, ctx);
-                ca_div_ui(res, res, 2, ctx);
+                ca_phi(res, ctx);
                 return 1;
             case FEXPR_Infinity:
                 ca_pos_inf(res, ctx);

doc/source/ca.rst

@@ -349,6 +349,10 @@ Special values
     Sets *res* to Euler's constant `\gamma`. This creates an element
     of the (transcendental?) number field `\mathbb{Q}(\gamma)`.
 
+.. function:: void ca_phi(ca_t res, ca_ctx_t ctx)
+
+    Sets *res* to the golden ratio `\varphi`.
+
 .. function:: void ca_unknown(ca_t res, ca_ctx_t ctx)
 
     Sets *res* to the meta-value *Unknown*.

examples/golden_ratio.c

@@ -0,0 +1,64 @@
+/* This file is public domain. Author: Raoul Bourquin. */
+
+#include "ca.h"
+
+
+void main_fexpr()
+{
+    fexpr_t Phi;
+    fexpr_init(Phi);
+
+    flint_printf("Evaluating Phi as fexpr:\n");
+
+    fexpr_set_symbol_str(Phi, "GoldenRatio");
+
+    fexpr_print(Phi);
+    printf("\n\n");
+
+    fexpr_clear(Phi);
+}
+
+
+void main_ca()
+{
+    ca_ctx_t ctx;
+    ca_t Phi;
+    ca_ctx_init(ctx);
+    ca_init(Phi, ctx);
+
+    flint_printf("Evaluating Phi as ca:\n");
+
+    ca_phi(Phi, ctx);
+
+    ca_print(Phi, ctx);
+    printf("\n\n");
+
+    ca_clear(Phi, ctx);
+}
+
+
+void main_qqbar()
+{
+    qqbar_t Phi;
+    qqbar_init(Phi);
+
+    flint_printf("Evaluating Phi as qqbar:\n");
+
+    qqbar_phi(Phi);
+
+    qqbar_printn(Phi, 50);
+    printf("\n");
+
+    qqbar_clear(Phi);
+}
+
+
+int main(int argc, char *argv[])
+{
+  main_fexpr();
+  main_ca();
+  main_qqbar();
+
+  flint_cleanup();
+  return EXIT_SUCCESS;
+}