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 =        1.644918809014074
  Error    = 1.525783415234905e-05
  Time     = 6.344660043716431

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 =        1.644918809014445
  Error    = 1.525783378109047e-05
  Time     = 3.250334978103638

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 =          1.6449188090143
  Error    = 1.525783392630764e-05
  Time     = 3.290994882583618