def z_high(x):
"""Returns right-hand tail of z distribution (0 to x).
x ranges from -infinity to +infinity; result ranges from 0 to 1
See Cephes docs for details."""
y = x * SQRTH
z = abs(y)
if z < SQRTH:
return 0.5 - 0.5 * erf(y)
else:
if x < 0:
return 1 - 0.5 * erfc(z)
else:
return 0.5 * erfc(z)
def z_low(x):
"""Returns left-hand tail of z distribution (0 to x).
x ranges from -infinity to +infinity; result ranges from 0 to 1
See Cephes docs for details."""
y = x * SQRTH
z = abs(y) #distribution is symmetric
if z < SQRTH:
return 0.5 + 0.5 * erf(y)
else:
if y > 0:
return 1 - 0.5 * erfc(z)
else:
return 0.5 * erfc(z)