Variables
 x1 in [-1,1],
 x2 in [-1,1],
 x3 in [-1,1],
 x4 in [-1,1],
 x5 in [-1,1],
 x6 in [-1,1],
 x7 in [-1,1],
 x8 in [-1,1];

Constraints
  4.731e-03*x1*x2 - 0.3578*x2*x3 - 0.1238*x1
  +x7 - 1.637e-03*x2 - 0.9338*x4 - 0.3571  =0,

  0.2238*x1*x3 + 0.7623*x2*x3 + 0.2638*x1
  -x7 - 0.07745*x2 - 0.6734*x4 - 0.6022  =0,

  x6*x8 + 0.3578*x1 + 4.731e-03*x2 =0,

  -0.7623*x1 + 0.2238*x2 + 0.3461 =0,

  x1^2 +x2^2 = 1,

  x3^2 +x4^2 = 1, 

  x5^2 +x6^2 = 1,

  x7^2 +x8^2 = 1;
