Another stab at toroid example

examples/magnet/toroid2.geo

@@ -0,0 +1,76 @@
+/////////////////////////
+// Geometric Inputs
+
+radius = 3.25;
+blc = radius/1;
+Box = 3*radius;
+lc = radius/1;
+
+ts = 1;         // height of toroid
+tx = radius;    // radial width of toroid, measured in centre of ring
+tl = 0;         // centre of rotation
+
+/////////////////////////////////////
+// Large Bounding box
+X0 = -Box;
+X1 =  Box;
+Y0 = -Box;
+Y1 =  Box;
+Z0 = -Box;
+Z1 =  Box;
+
+pp = newp;
+Point(pp)    = {X0, Y0, Z0, blc};
+Point(pp+1)  = {X1, Y0, Z0, blc};
+Point(pp+2)  = {X1, Y1, Z0, blc};
+Point(pp+3)  = {X0, Y1, Z0, blc};
+
+lv = newl;
+Line(lv) = {pp,pp+1};
+Line(lv+1) = {pp+1,pp+2};
+Line(lv+2) = {pp+2,pp+3};
+Line(lv+3) = {pp+3,pp};
+Line Loop(lv+4) = {lv, lv+1, lv+2, lv+3};
+
+bs = news;
+Plane Surface(bs) = {lv+4};
+v[] = Extrude {0, 0, Z1-Z0} { Surface{bs}; };
+
+/////////////////////////////////////////
+// Make a toroid
+tpp = newp;
+Point(tpp  ) = {    tx,    0, 0,  lc};
+Point(tpp+1) = { ts+tx,    0, 0,  lc};
+Point(tpp+2) = {    tx,   ts, 0,  lc};
+Point(tpp+3) = {    tx,  -ts, 0,  lc};
+Point(tpp+4) = {-ts+tx,    0, 0,  lc};
+
+cc = newc;
+Circle(cc  ) = {tpp+1, tpp, tpp+2};
+Circle(cc+1) = {tpp+2, tpp, tpp+4};
+Circle(cc+2) = {tpp+4, tpp, tpp+3};
+Circle(cc+3) = {tpp+3, tpp, tpp+1};
+
+ll = newll;
+Line Loop(ll) = {cc, cc+1, cc+2, cc+3};
+rs = news;
+
+ps = news;
+Plane Surface(ps) = {ll};
+
+tv1[] = Extrude {{0, 1, 0},{-tl,0,0}, 2*Pi/3} { Surface{ps}    ;};
+tv2[] = Extrude {{0, 1, 0},{-tl,0,0}, 2*Pi/3} { Surface{tv1[0]};};
+tv3[] = Extrude {{0, 1, 0},{-tl,0,0}, 2*Pi/3} { Surface{tv2[0]};};
+
+cv = newv;
+Compound Volume(cv) = {tv1[1], tv2[1], tv3[1] };
+
+//cs = news;
+//Compound Surface(cs) = {tv1[0], tv2[0], tv3[0] };
+
+// Not correct?
+Surface{tv1[0]} In Volume{v[1]};
+//Surface{tv2[0]} In Volume{v[1]};
+//Surface{tv3[0]} In Volume{v[1]};
+
+Physical Volume(1) = {v[1]};