[R] Tick marks for abline
ihaka at stat.auckland.ac.nz
Thu Oct 26 22:11:48 CEST 2000
On Thu, Oct 26, 2000 at 11:29:18AM -0500, Erin Hodgess wrote:
> I am drawing graphs for a College Algebra class. I would like to have
> the x and y axes, along with the lines that I am plotting. So I leave
> off the axes, and use xlim and ylim. Then I add my abline(v=0).
> However, I would like to have tick marks on the abline. How would I do
> that, please?
Here is an example of drawing a cubic with axes in the middle of the
# Draw the basic curve (limits were established by trial and error).
# The axes are turned off blank axis labels used.
curve(x * (2 * x - 3) * (2 * x + 3), from = -1.85, to = 1.85,
xlim = c(-2, 2), ylim = c(-10, 10),
axes = FALSE, xlab = "", ylab = "")
# Draw the axes at the specified positions (crossing at (0, 0)).
# The ticks positions are specified (those at (0,0) are omitted).
# Note the use of las=1 to produce horizontal tick labels on the
# vertical axis.
axis(1, pos = 0, at = c(-2, -1, 1, 2))
axis(2, pos = 0, at = c(-10, -5, 5, 10), las = 1)
# Use the mathematical annotation facility to label the plot.
title(main = expression(italic(y==x * (2 * x - 3) * (2 * x + 3))))
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