R devel - May 2005 - Reversing axis in a log plot (PR#7894)

Full_Name: Christian Marquardt
Version: 2.1.0
OS: Linux (Redhat 9)
Submission from: (NULL) (151.170.240.10)


Following the advice of a reader of R-help, I would now like to submit this as a
bug report:

Say we have

  x = seq(1,3, by = 0.01)
  y = exp(x)

Plotting and reversing linear axis is fine

   plot(x,y)
   plot(x,y, ylim = c(30,1))

as is a usual log-plot:

  plot(x,y, log = "y", ylim = c(1,30))

However,

  plot(x,y, log = "y", ylim = c(30,1))

fails with

  Error in axis(2, ...) : log - axis(), 'at' creation, _SMALL_ range:
invalid {xy}axp or par;
         axp[0]= 10, usr[0:1]=(34.3721,0.872801)
  In addition: Warning message:
  CreateAtVector "log"(from axis()): usr[0] = 34.3721 > 0.872801 =
usr[1] !


According to Petr Pikal <petr.pikal -at- precheza.cz>, replacing the ylim
argument by ylim = c(30,1.2) helps in the above example; but in my real world
applications, it's actually difficult to find a working value for ylim.

I hope this is useful,

  Christian.

Yes, this one is a bug in CreateAtVector, plot.c.
It already has the lines:


     /* Debugging: When does the following happen... ? */
     if (umin > umax)
         warning("CreateAtVector \"log\"(from axis()): "
             "usr[0] = %g > %g = usr[1] !", umin, umax);


And now we know that it happens if (and only if?????) the logarithmic 
scale is not very small (i.e. axp[2] > 0, this is equal to R's 
par("yaxp")[3] in your example) and the axis are reversed (umin >
umax).

I'll try to provide a fix which should be possible by reversing 
arguments axp and usr in this case and returning a reversed at ...

Uwe Ligges




marquardt.christian@gmail.com wrote:
> Full_Name: Christian Marquardt
> Version: 2.1.0
> OS: Linux (Redhat 9)
> Submission from: (NULL) (151.170.240.10)
> 
> Following the advice of a reader of R-help, I would now like to submit this
as a
> bug report:
> 
> Say we have
> 
>   x = seq(1,3, by = 0.01)
>   y = exp(x)
> 
> Plotting and reversing linear axis is fine
> 
>    plot(x,y)
>    plot(x,y, ylim = c(30,1))
> 
> as is a usual log-plot:
> 
>   plot(x,y, log = "y", ylim = c(1,30))
> 
> However,
> 
>   plot(x,y, log = "y", ylim = c(30,1))
> 
> fails with
> 
>   Error in axis(2, ...) : log - axis(), 'at' creation, _SMALL_
range:
> invalid {xy}axp or par;
>          axp[0]= 10, usr[0:1]=(34.3721,0.872801)
>   In addition: Warning message:
>   CreateAtVector "log"(from axis()): usr[0] = 34.3721 >
0.872801 = usr[1] !
> 
> 
> According to Petr Pikal <petr.pikal -at- precheza.cz>, replacing the
ylim
> argument by ylim = c(30,1.2) helps in the above example; but in my real
world
> applications, it's actually difficult to find a working value for ylim.
> 
> I hope this is useful,
> 
>   Christian.
> 
> ______________________________________________
> R-devel@stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

Please find attached my proposal for a bugfix. The experts might to 
better, though.

Uwe Ligges



ligges@statistik.uni-dortmund.de wrote:
> Yes, this one is a bug in CreateAtVector, plot.c.
> It already has the lines:
> 
> 
>      /* Debugging: When does the following happen... ? */
>      if (umin > umax)
>          warning("CreateAtVector \"log\"(from axis()):
"
>              "usr[0] = %g > %g = usr[1] !", umin, umax);
> 
> 
> And now we know that it happens if (and only if?????) the logarithmic 
> scale is not very small (i.e. axp[2] > 0, this is equal to R's 
> par("yaxp")[3] in your example) and the axis are reversed (umin
> umax).
> 
> I'll try to provide a fix which should be possible by reversing 
> arguments axp and usr in this case and returning a reversed at ...
> 
> Uwe Ligges
> 
> 
> 
> 
> marquardt.christian@gmail.com wrote:
> 
> 
>>Full_Name: Christian Marquardt
>>Version: 2.1.0
>>OS: Linux (Redhat 9)
>>Submission from: (NULL) (151.170.240.10)
>>
>>Following the advice of a reader of R-help, I would now like to submit
this as a
>>bug report:
>>
>>Say we have
>>
>>  x = seq(1,3, by = 0.01)
>>  y = exp(x)
>>
>>Plotting and reversing linear axis is fine
>>
>>   plot(x,y)
>>   plot(x,y, ylim = c(30,1))
>>
>>as is a usual log-plot:
>>
>>  plot(x,y, log = "y", ylim = c(1,30))
>>
>>However,
>>
>>  plot(x,y, log = "y", ylim = c(30,1))
>>
>>fails with
>>
>>  Error in axis(2, ...) : log - axis(), 'at' creation, _SMALL_
range:
>>invalid {xy}axp or par;
>>         axp[0]= 10, usr[0:1]=(34.3721,0.872801)
>>  In addition: Warning message:
>>  CreateAtVector "log"(from axis()): usr[0] = 34.3721 >
0.872801 = usr[1] !
>>
>>
>>According to Petr Pikal <petr.pikal -at- precheza.cz>, replacing
the ylim
>>argument by ylim = c(30,1.2) helps in the above example; but in my real
world
>>applications, it's actually difficult to find a working value for
ylim.
>>
>>I hope this is useful,
>>
>>  Christian.
>>
>>______________________________________________
>>R-devel@stat.math.ethz.ch mailing list
>>https://stat.ethz.ch/mailman/listinfo/r-devel
> 
> 
> ______________________________________________
> R-devel@stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

>>>>> "UweL" == Uwe Ligges
<ligges@statistik.uni-dortmund.de>
>>>>>     on Fri, 27 May 2005 11:42:54 +0200 (CEST) writes:
    UweL> Please find attached my proposal for a bugfix. The
    UweL> experts might to better, though.

    UweL> Uwe Ligges

Thank you, Uwe!

Yes, your fix works, and yes, it can be improved (e.g., no need for
the 'atr'; no 'reversed' when in the linear case, ..)

Also, there won't be any warning either anymore,
since
	plot(1:3, exp(1:3), xlim = c(30,1))
also gives no warning.

You'll find the fixed plot.c in tomorrow's snapshot.

Martin

BTW:  The whole thing {axis reversion} doesn't work in S-plus
      {doing a non-sensical plot, with tons of warnings}