function res = exact1(x)
  t1  = exp(0.5);
  t3  = sqrt(2);
  t5  = erf(t3 / 2);
  t10 = erf(x .* t3 / 2);
  t11 = x .^ 2;
  t13 = exp(t11 / 2 - 1 / 2);
  t17 = exp(t11 / 2);
  res = t13 .* t10 ./ t5 .* (3 - t1) + t17 - 1 ;
end