From jason@cs.rochester.edu  Mon Feb  5 01:17:21 2001
From: jason@cs.rochester.edu (jason@cs.rochester.edu)
Date: Mon, 5 Feb 2001 02:17:21 +0100 (MET)
Subject: [Rd] clipped lines have wrong slope in log plot (PR#839)
Message-ID: <200102050117.CAA29241@pubhealth.ku.dk>

Hi,

I'm using R version 1.2.0 (2000-12-15), on RedHat Linux 6.2 (kernel 2.2.14).

The following command ought to plot a straight-line on a log-log
graph but instead plots two line segments, both with the wrong
slope:

  plot(c(1,10,100),c(100,10,1),type="l",xlim=c(1,20),ylim=c(1,20),log="xy")

Only clipped lines seem to have this problem.  Changing to type "b"
or enlarging the ranges fixes it:

  plot(c(1,10,100),c(100,10,1),type="b",xlim=c(1,20),ylim=c(1,20),log="xy")
  plot(c(1,10,100),c(100,10,1),type="l",xlim=c(1,100),ylim=c(1,100),log="xy")

abline has the same problem.  Try following the above calls with abline(2,-1).
(This is supposed to plot a straight line in the log-log domain, and
does, but it's the wrong straight line.)

I can also get the problem where only one axis is logarithmic.  
Let's untransform the x-axis from the original command:
 
  plot(log(c(1,10,100)),c(100,10,1),type="l",xlim=log(c(1,20)),ylim=c(1,20),log="y")

Thanks! - Jason Eisner






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[Rd] clipped lines have wrong slope in log plot (PR#839)
jason@cs.rochester.edu