QUAD2D_OPEN_MP:
  C++/OpenMP version
  Estimate the integral of f(x,y) over [0,1]x[0,1].
  f(x,y) = 1 / ( 1 - x * y ).

  A        = 0
  B        = 1
  NX       = 32768
  NY       = 32768
  N        = 1073741824
  Exact    =        1.644934066848226

  Estimate =        1.644918809012695
  Error    = 1.525783553146809e-05
  Time     = 133.7981669902802

QUAD2D_OPEN_MP:
  C++/OpenMP version
  Estimate the integral of f(x,y) over [0,1]x[0,1].
  f(x,y) = 1 / ( 1 - x * y ).

  A        = 0
  B        = 1
  NX       = 32768
  NY       = 32768
  N        = 1073741824
  Exact    =        1.644934066848226

  Estimate =        1.644918809014846
  Error    = 1.525783338029996e-05
  Time     = 68.96735000610352

QUAD2D_OPEN_MP:
  C++/OpenMP version
  Estimate the integral of f(x,y) over [0,1]x[0,1].
  f(x,y) = 1 / ( 1 - x * y ).

  A        = 0
  B        = 1
  NX       = 32768
  NY       = 32768
  N        = 1073741824
  Exact    =        1.644934066848226

  Estimate =        1.644918809014969
  Error    = 1.525783325773133e-05
  Time     = 68.96791100502014