// 双线回路 2D 磁静场：能量法提电感（教材算例）
// 两根 1×1mm 方截面导体，中心距 d=10mm，电流 ±z；空气域 ±60mm
lc = 0.15e-3; lca = 6e-3; a = 0.5e-3; d = 5e-3; D = 60e-3;
// 导体1（+z）
Point(1) = {-d-a,-a,0,lc}; Point(2) = {-d+a,-a,0,lc}; Point(3) = {-d+a,a,0,lc}; Point(4) = {-d-a,a,0,lc};
// 导体2（-z）
Point(5) = {d-a,-a,0,lc}; Point(6) = {d+a,-a,0,lc}; Point(7) = {d+a,a,0,lc}; Point(8) = {d-a,a,0,lc};
// 空气外框
Point(9) = {-D,-D,0,lca}; Point(10) = {D,-D,0,lca}; Point(11) = {D,D,0,lca}; Point(12) = {-D,D,0,lca};
Line(1) = {1,2}; Line(2) = {2,3}; Line(3) = {3,4}; Line(4) = {4,1};
Line(5) = {5,6}; Line(6) = {6,7}; Line(7) = {7,8}; Line(8) = {8,5};
Line(9) = {9,10}; Line(10) = {10,11}; Line(11) = {11,12}; Line(12) = {12,9};
Curve Loop(1) = {1,2,3,4}; Plane Surface(1) = {1};
Curve Loop(2) = {5,6,7,8}; Plane Surface(2) = {2};
Curve Loop(3) = {9,10,11,12};
Plane Surface(3) = {3,1,2};
Physical Surface(101) = {1};   // CoilPlus
Physical Surface(102) = {2};   // CoilMinus
Physical Surface(103) = {3};   // Air
Physical Line(200) = {9,10,11,12}; // 外边界 A=0