Update MetaPost to Asymptote in Serway and Jewett v4's problem 19.15.

diff --git a/latex/problems/Serway_and_Jewett_4/problem19.15.tex b/latex/problems/Serway_and_Jewett_4/problem19.15.tex
index e927f4a2fe1d3665d433429b326d49f336a827a0..1e2156fe6f5b6086cf3d45bad806c305c58787be 100644 (file)
--- a/latex/problems/Serway_and_Jewett_4/problem19.15.tex
+++ b/latex/problems/Serway_and_Jewett_4/problem19.15.tex
@@ -6,49 +6,42 @@ at the location of charge $q_4$.
 \Part{b} What is the resultant force on $q_4$?
 \end{problem*} % problem 19.15
 
-\empaddtoprelude{
-  numeric a;
-  pair A, B, C, D;
-  a := 1cm;
-  A := (0, a); % q1, labeled CCW from upper left
-  B := origin; % q2
-  C := (a, 0); % q3
-  D := (a, a); % q4
-  def drawE = 
-    label.lft("a", draw_length(A, B, 8pt));
-    label.bot("a", draw_length(B, C, 8pt));
-    labeloffset := 5pt;
-    draw_pcharge(A, 3pt);
-    label.bot(btex $q_1$ etex, A);
-    draw_pcharge(B, 3pt);
-    label.top(btex $q_2$ etex, B);
-    draw_pcharge(C, 3pt);
-    label.top(btex $q_3$ etex, C);
-    draw_pcharge(D, 3pt);
-    label.bot(btex $q_4$ etex, D);
-  enddef;
-}
 \begin{nosolution}
 \begin{center}
-\begin{empfile}[5ns]
-\begin{emp}(0cm,0cm)
-  drawE;
-\end{emp}
-\end{empfile}
+\begin{asy}
+import ElectroMag;
+
+real u = 2cm;
+draw(scale(u)*unitsquare, dashed);
+Charge a = aCharge((0, u), q=2, Label("$q_1$", align=W));  a.draw();
+Charge b = aCharge((0, 0), q=3, Label("$q_2$", align=W));  b.draw();
+Charge c = aCharge((u, 0), q=4, Label("$q_3$", align=E));  c.draw();
+Charge d = aCharge((u, u), q=4, Label("$q_4$", align=E));  d.draw();
+label("$a$", (u/2, 0), align=S);
+\end{asy}
 \end{center}
 \end{nosolution}
 
 \begin{solution}
 \begin{center}
-\begin{empfile}[5]
-\begin{emp}(0cm,0cm)
-  label.rt(btex $E_{14}$ etex, draw_Efield(A, D, 0.5cm));
-  label.urt(btex $E_{24}$ etex, draw_Efield(B, D, 0.53cm));
-  label.lft(btex $E_{34}$ etex, draw_Efield(C, D, 1cm));
-  draw_ijhats((-1.5*a, a/3), 0, a/3);
-  drawE;
-\end{emp}
-\end{empfile}
+\begin{asy}
+import ElectroMag;
+
+real u = 2cm;
+draw(scale(u)*unitsquare, dashed);
+Charge a = aCharge((0, u), q=2, Label("$q_1$", align=W));  a.draw();
+Charge b = aCharge((0, 0), q=3, Label("$q_2$", align=W));  b.draw();
+Charge c = aCharge((u, 0), q=4, Label("$q_3$", align=E));  c.draw();
+Charge d = aCharge((u, u), q=1, Label("$q_4$", align=SE));  d.draw();
+label("$a$", (u/2, 0), align=S);
+Charge cs[] = {a, b, c};
+CoulombEFields(d.center(), cs, scale=u, unit=u/4);
+Vector F = CoulombForce(a, d, scale=u, unit=u/4)
+         + CoulombForce(b, d, scale=u, unit=u/4)
+         + CoulombForce(c, d, scale=u, unit=u/4);
+F.label = Label("$F$", position=EndPoint, align=RightSide);
+F.draw();
+\end{asy}
 \end{center}
 Let \ihat\ point to the right and \jhat\ point up.
 \begin{equation}