<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; charset=iso-8859-1"> <META content="MSHTML 6.00.6000.16640" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV><FONT face=Arial size=2>After playing a litle with procedure log i found:</FONT></DIV> <DIV><FONT face=Arial size=2>(1) (log positive-exact-integer) never returns +inf.0 (although some time may be required, especially during compilation, for exponents beyond one million)</FONT></DIV> <DIV><FONT face=Arial size=2>(2) (log positive-exact-rational) may return +inf.0, even when log does not return +inf.0 for larger exact integers.</FONT></DIV> <DIV><FONT face=Arial size=2>(3) Therefore I use (let ((x (inexact->exact x))) (- (log (numerator x)) (log (denominator x)) for any real x.</FONT></DIV> <DIV><FONT face=Arial size=2>(4) I ignore the fact that even the log may be too big for a floating point. Anyway, when that is the case log does not return before exhausting my patience, which is quite acceptible of course (I mean the not returning, not my impatience:)</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>Questions:</FONT></DIV> <DIV><FONT face=Arial size=2>(1) is this a correct approach (i.e. may I assume that PLT scheme's log does not produce +inf.0 on very large exact integer numbers? (as long as the log does not exceed 1e234)</FONT></DIV> <DIV><FONT face=Arial size=2>(2) is there somewhere a solidly based (integer-log positive-exact-integer-n) function that returns the greatest exact natural number p such that (expt e p)<=n?</FONT></DIV> <DIV><FONT face=Arial size=2>(3) An absolute error less than a few units would not be a problem. I can always make a few steps up or down afterwards.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>In fact I use base 10 logs, but thats only a matter of scaling.</FONT></DIV> <DIV><FONT face=Arial size=2></FONT> </DIV> <DIV><FONT face=Arial size=2>I am speaking about Welcome to DrScheme, version 3.99.0.23-svn22apr2008 [3m].</FONT></DIV> <DIV><FONT face=Arial size=2>Jos</FONT></DIV></BODY></HTML>