Update MetaPost to Asymptote in Serway and Jewett v4's problem 19.16.

diff --git a/latex/problems/Serway_and_Jewett_4/problem19.16.tex b/latex/problems/Serway_and_Jewett_4/problem19.16.tex
index 9e8e9d34246ec2f1753b72aa677b2e8f86663f3d..55524247a83219a9c048e51ac1f564d0046ceeaa 100644 (file)
--- a/latex/problems/Serway_and_Jewett_4/problem19.16.tex
+++ b/latex/problems/Serway_and_Jewett_4/problem19.16.tex
@@ -4,46 +4,44 @@ electric field at a distant point on the $+x$ axis is $E_x \approx
 4k_eqa/x^3$.
 \end{problem*} % problem 19.16
 
-\empaddtoprelude{
-  pair A, B;
-  numeric a;
-  a := 1cm;
-  A := (-a,0);
-  B := (a, 0);
-  C := (6a, 0);
-  def drawC = 
-    drawarrow (A-(a,0))--(C+(a,0)) withpen pencircle scaled 0pt;
-    draw_ncharge(A, 6pt);
-    draw_pcharge(B, 6pt);
-    label.top("0", draw_ltic(origin, 90, 0, 3pt, 0pt, black));
-    dotlabel.bot("x", C);
-    label.bot("a", draw_length(A, origin, 10pt));
-    label.bot("a", draw_length(origin, B, 10pt));
-    labeloffset := 8pt;
-    label.top("-q", A);
-    label.top("q", B);
-  enddef;
-}
-
 \begin{nosolution}
 \begin{center}
-\begin{empfile}[3p]
-\begin{emp}(0cm, 0cm)
-  drawC;
-\end{emp}
-\end{empfile}
+\begin{asy}
+import ElectroMag;
+
+real u = 0.5cm;
+Vector ihat = ihat();
+ihat.mag = 4u;
+ihat.label = Label("$x$", position=EndPoint, align=RightSide);
+ihat.draw();
+Charge a = nCharge((-u, 0), Label("$-q$", align=S));  a.draw();
+Charge b = pCharge((u, 0), Label("$+q$", align=S));  b.draw();
+Distance da = Distance(a.center(), (0,0), "$a$", offset=-12pt);  da.draw();
+Distance db = Distance((0,0), b.center(), "$a$", offset=-12pt);  db.draw();
+\end{asy}
 \end{center}
 \end{nosolution}
 
 \begin{solution}
 \begin{center}
-\begin{empfile}[3]
-\begin{emp}(0cm, 0cm)
-  label.top(btex $E_{q}$ etex, draw_Efield(B, C, 18pt));
-  label.top(btex $E_{-q}$ etex, draw_Efield(A, C, -16pt));
-  drawC;
-\end{emp}
-\end{empfile}
+\begin{asy}
+import ElectroMag;
+
+real u = 0.5cm;
+Vector ihat = ihat();
+ihat.mag = 9u;
+ihat.label = Label("$x$", position=EndPoint, align=RightSide);
+ihat.draw();
+Charge a = nCharge((-u, 0), Label("$-q$", align=S));  a.draw();
+Charge b = pCharge((u, 0), Label("$+q$", align=S));  b.draw();
+Distance da = Distance(a.center(), (0,0), "$a$", offset=-12pt);  da.draw();
+Distance db = Distance((0,0), b.center(), "$a$", offset=-12pt);  db.draw();
+Charge cs[] = {a, b};
+string subscripts[] = {"-", "+"};
+pair c = (6u, 0);
+CoulombEFields(c, cs, subscripts, scale=c.x, unit=u);
+dot(c);
+\end{asy}
 \end{center}
 Let us assume the point in question has a positive $x$ value (just
 reverse the sign if $x < 0$).