1) Variance as error estimate
---- integral from 0 to 1 of x ------  acc= 1e-05  eps= 0
exact = 0.5
result= 0.5000021439013008  npoints= 8184
---- integral from 0 to 1 of sqrt(x) ------  acc= 1e-05  eps= 0
exact = 0.6666666666666666
result= 0.6666669358643285  npoints= 8952
---- clenshaw-curtis integral from 0 to 1 of 1/sqrt(x) ------  acc= 1e-05  eps= 0
exact = 2
result= 1.9999977840321153  npoints= 19432

2) Difference between averages as error estimate
---- integral from 0 to 1 of x ------  acc= 1e-05  eps= 0
exact = 0.5
result= 0.5001924103587267  npoints= 10168
---- integral from 0 to 1 of sqrt(x) ------  acc= 1e-05  eps= 0
exact = 0.6666666666666666
result= 0.6666937175896985  npoints= 10840
---- clenshaw-curtis integral from 0 to 1 of 1/sqrt(x) ------  acc= 1e-05  eps= 0
exact = 2
result= 1.9999781035626287  npoints= 23048