evalf.py 文件源码

def evalf_log(expr, prec, options):
    from sympy import Abs, Add, log
    if len(expr.args)>1:
        expr = expr.doit()
        return evalf(expr, prec, options)
    arg = expr.args[0]
    workprec = prec + 10
    xre, xim, xacc, _ = evalf(arg, workprec, options)

    if xim:
        # XXX: use get_abs etc instead
        re = evalf_log(
            log(Abs(arg, evaluate=False), evaluate=False), prec, options)
        im = mpf_atan2(xim, xre or fzero, prec)
        return re[0], im, re[2], prec

    imaginary_term = (mpf_cmp(xre, fzero) < 0)

    re = mpf_log(mpf_abs(xre), prec, rnd)
    size = fastlog(re)
    if prec - size > workprec and re != fzero:
        # We actually need to compute 1+x accurately, not x
        arg = Add(S.NegativeOne, arg, evaluate=False)
        xre, xim, _, _ = evalf_add(arg, prec, options)
        prec2 = workprec - fastlog(xre)
        # xre is now x - 1 so we add 1 back here to calculate x
        re = mpf_log(mpf_abs(mpf_add(xre, fone, prec2)), prec, rnd)

    re_acc = prec

    if imaginary_term:
        return re, mpf_pi(prec), re_acc, prec
    else:
        return re, None, re_acc, None