From a0e1da74b042bd5faf026aa6fd42310ceb424ace Mon Sep 17 00:00:00 2001
From: "W. Trevor King" <wking@drexel.edu>
Date: Wed, 11 Apr 2012 17:52:42 -0400
Subject: [PATCH] Add optional subscript override to Coulomb labels in
 Mechanics.asy.

---
 asymptote/ElectroMag-test.asy |  5 +++--
 asymptote/ElectroMag.asy      | 29 +++++++++++++++++++++++------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/asymptote/ElectroMag-test.asy b/asymptote/ElectroMag-test.asy
index 5b761f4..ec4820b 100644
--- a/asymptote/ElectroMag-test.asy
+++ b/asymptote/ElectroMag-test.asy
@@ -25,6 +25,7 @@ Charge a = pCharge(center=(0.5u,2u));
 Charge b = aCharge(center=(0,-0.5u), q=1);
 Charge c = nCharge(center=(-3u,-0.5u), q=-3);
 Charge cs[] = {a,b,c};
+string subscripts[] = {"a"};
 Distance dab = Distance(b.center(), a.center(), scale=u, L="$r_1$");
 Distance dbc = Distance(c.center(), b.center(), scale=u, L="$r_2$");
 Distance ds[] = {dab};
@@ -43,10 +44,10 @@ for (int i=0; i<ds.length; i+=1)
 for (int i=0; i<as.length; i+=1)
   as[i].draw();
 
-CoulombEFields((-0.5u, 1.2u), c=cs, scale=2u, unit=u/2);
+CoulombEFields((-0.5u, 1.2u), c=cs, subscripts=subscripts, scale=2u, unit=u/2);
 //Vector Fba = CoulombForce(b,a, scale=2u, unit=u);
 //Fba.draw();
-CoulombForces(c=cs, scale=2u, unit=u);
+CoulombForces(c=cs, subscripts=subscripts, scale=2u, unit=u);
 
 Charge a = aCharge(center=(-2u, 2u), q=0);
 a.draw();
diff --git a/asymptote/ElectroMag.asy b/asymptote/ElectroMag.asy
index 5495cf1..2a78182 100644
--- a/asymptote/ElectroMag.asy
+++ b/asymptote/ElectroMag.asy
@@ -122,12 +122,18 @@ Vector CoulombEField(pair a, Charge b, Label L="", real scale=1mm,
   return v;
 }
 
-void CoulombEFields(pair a, Charge c[], real scale=1mm, real unit=1mm)
+void CoulombEFields(pair a, Charge c[], string subscripts[]={}, real scale=1mm,
+                    real unit=1mm)
 {
   Vector E;
-  string s;
+  string s, sub;
   for (int i=0; i<c.length; i+=1) {
-    s = "$E_{" + format("%d", i+1) + "}$";
+    if (i < subscripts.length) {
+      sub = subscripts[i];
+    } else {
+      sub = format("%d", i+1);
+    }
+    s = "$E_{" + sub + "}$";
     E = CoulombEField(
         a, c[i], L=Label(s, position=EndPoint, align=LeftSide),
         scale=scale, unit=unit);
@@ -148,14 +154,25 @@ Vector CoulombForce(Charge a, Charge b, Label L="", real scale=1mm, real unit=1m
   return v;
 }
 
-void CoulombForces(Charge c[], real scale=1mm, real unit=1mm)
+void CoulombForces(Charge c[], string subscripts[]={}, real scale=1mm,
+                   real unit=1mm)
 {
   Vector F;
-  string s;
+  string s, subi, subj;
   for (int i=0; i<c.length; i+=1) {
+    if (i < subscripts.length) {
+      subi = subscripts[i];
+    } else {
+      subi = format("%d", i+1);
+    }
     for(int j=0; j<c.length; j+=1) {
       if (i==j) continue;
-      s = "$F_{" + format("%d", i+1) + "," + format("%d", j+1) + "}$";
+      if (j < subscripts.length) {
+        subj = subscripts[j];
+      } else {
+        subj = format("%d", j+1);
+      }
+      s = "$F_{" + subi + "," + subj + "}$";
       F = CoulombForce(
           c[i], c[j], L=Label(s, position=EndPoint, align=LeftSide),
           scale=scale, unit=unit);
-- 
2.26.2