chebyu/chebyt fail at infinity #469
Description
Good:
>>> mpmath.chebyu(4,1e4)
mpf('1.599999988e+17')
>>> mpmath.chebyu(4,1e5)
mpf('1.5999999998799999e+21')
>>> mpmath.chebyu(4,1e100)
mpf('1.6000000000000002e+401')
bad:
>>> mpmath.chebyu(4,float('inf'))
mpf('5.0')
The expected answer is mpf('+inf'). Instead it seems to give n+1: haven't debugged it any further than that.