'magnet
   '        09/08/1993


    DIM a(5), xc(5), zc(5), al(5), in(5)
    DIM i AS INTEGER, nb AS INTEGER, ib AS INTEGER

    CONST pi = 3.14159265#, deuxpi = 2 * pi
    CONST degrad = pi / 180!
    CONST dt = 2 * pi / 15


    CLS
       READ nb
       FOR i = 1 TO nb
          READ a(i), zc(i), xc(i), al(i), in(i)
          al(i) = al(i) * degrad
       NEXT i
       SCREEN 2
       FOR x = -110 TO 110 STEP 10.1
            FOR z = 0 TO 400 STEP 10.1
               bx = 0
               bz = 0
               FOR ib = 1 TO nb
                 GOSUB calculs
              NEXT ib
              xp = z + 10
              yp = x + 120
              b = SQR(bx * bx + bz * bz)
              IF (b > .1) THEN
                  bx = bx * .1 / b
                  bz = .1 * bz / b
               END IF
               IF (b < .03) THEN
                  bx = bx * .3 / b
                  bz = .3 * bz / b
               END IF
               x2 = xp + bz * 100
               y2 = yp + bx * 100
               LINE (xp, yp)-(x2, y2)
            NEXT z
       NEXT x
       a$ = INPUT$(1)
       CLS
       SCREEN 0
       END
       

calculs:
       FOR th = 0 TO deuxpi STEP dt
           lx = -a(ib) * SIN(th) * COS(al(ib)) * dt
           ly = a(ib) * COS(th) * dt
           lz = -a(ib) * SIN(th) * SIN(al(ib)) * dt
           rx = x - (xc(ib) + a(ib) * COS(th) * COS(al(ib)))
           ry = -a(ib) * SIN(th)
           rz = z - (zc(ib) + a(ib) * COS(th) * SIN(al(ib)))
           dx = ly * rz - lz * ry
           dz = lx * ry - ly * rx
           r = SQR(rx * rx + ry * ry + rz * rz)
           r3 = r * r * r
           bx = bx + in(ib) * dx / r3
           bz = bz + in(ib) * dz / r3
        NEXT th
     RETURN


 DATA 2
 DATA 5,100,50,45,0.01
 DATA 10,300,-50,45,0.1