[Rd] clipped lines have wrong slope in log plot (PR#839)

[jason@cs.rochester.edu]

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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