Hi all,
I have this code:
using Plots, LaTeXStrings
gr()
f(x)=floor(x)
plot(f,0,10,ylim=(-12,12))
Since [ x ] denotes the gretest integer less than or equal to x, I want to plot it like this:
Anyone know how?
One way:
using Plots; gr()
xp = [[i, i+1 - 5*eps()] for i in -12:11]
p = plot(ylim=(-12,12), framestyle = :origin)
for x in xp
plot!(x, floor.(x), c=:black)
scatter!(x, floor.(x), ms=3, msc=:black, mc=[:black, :white])
end
p
NB: it would be faster not to loop and plot everything in one go. It would require inserting NaNs at the breaks.
3 Likes
Creating step functions is not as simple as just using floor().
I tried to reproduce the original plot (not the best code, but it has been fun):
f(x) = floor(x)
x = -5:1:4
y = f.(x)
plot(x[1:2], [y[1], y[1]], label=L"f(x) = \lfloor x \rfloor", legend=:bottomleft,legend_foreground_color=:white, legend_font_color=:blue, color=:blue, showaxis=false, tickfontcolor=:white)
# axis and
hline!((0,0), color=:black, label="")
vline!((0,0), color=:black, label="")
for i in x
if i!= 0
annotate!(i,-0.2, (i, 7))
end
end
for i in y
if i != 0
annotate!(-.2, i, (i, 7))
end
end
annotate!(-.2, -.2, ("0", 7))
for i in 2:length(x)-1
plot!(x[i:i+1], [y[i], y[i]], label="", color=:blue, lw=2)
scatter!(x[i], y[i], marker=:circle, markersize=8, label="")
end
scatter!(x[1:end-1], y[1:end-1], markersize=3, markercolor=:blue, label="")
scatter!(x[2:end], y[1:end-1], markersize=3, markercolor=:white, label="")
1 Like
Here is a version without the plot loop using NaN at the breaks:
using Plots; gr()
x = -12:12
xp = [[i, i+1 - 5*eps(), NaN] for i in x[1:end-1]]
xx = collect(Iterators.flatten(xp))
yy = floor.(xx)
plot(xx, yy, c=:black, label=false, framestyle = :origin)
scatter!(xx', yy', msc=:black, mc=[:black :white :white], ms=3)
It is really beautiful,
I want to ask
plot(x[1:2], [y[1], y[1]]
why there are two y[1] ? I want to know the details behind it.
Note that if you want the axes centered at the origin, you should use plot argument: framestyle = :origin. NB: updated in examples above
Thanks for the explanation.
Because the first step goes from point (x[1], y[1]) to (x[2], y[1]). It’s the same for the rest of the steps inside the for loop.
I have cleaned my version a little bit (thanks to @rafael.guerra):
# Plot configuration
plot(legend_title=L"f(x) = \lfloor x \rfloor", legend=:bottomleft,legend_foreground_color=:white, legend_title_font_color=:blue, color=:blue, framestyle=:origin, ticks=x)
# Steps drawing
for i in 1:length(x)-1
plot!(x[i:i+1], [y[i], y[i]], label="", color=:blue, lw=2)
end
# Points at the beginning ot the steps
scatter!(x[1:end-1], y[1:end-1], markersize=3, markercolor=:blue, label="")
# End points
scatter!(x[2:end], y[1:end-1], markersize=3, markercolor=:white, label="")
# Adds '0' close to origin
annotate!(-.22, -.26, ("0", 8))
I’m sure it could be improved, but I think it’s quite close to the original.
2 Likes
Tried this in Jupyter Notebook and compare with your old code.
It is simpler, so we can remove the old
f(x) = floor(x)
x = -5:1:4
y = f.(x)
plot(x[1:2], [y[1], y[1]], label=L"f(x) = \lfloor x \rfloor", legend=:topleft,legend_foreground_color=:white, legend_font_color=:blue3, color=:blue3, showaxis=false, tickfontcolor=:white)
# axis and
hline!((0,0), color=:black, label="")
vline!((0,0), color=:black, label="")
for i in x
if i!= 0
annotate!(i,-0.2, (i, 7))
end
end
for i in y
if i != 0
annotate!(-.2, i, (i, 7))
end
end
for i in 2:length(x)-1
plot!(x[i:i+1], [y[i], y[i]], label="", color=:blue3, lw=2)
scatter!(x[i], y[i], marker=:circle, markersize=8, label="")
end
Hi!
One simple option is just changing the function to:
f(x) = floor(x + 1/2)
And the step of the x to 0.5:
x = -5:.5:4
In this case, you’ll get:
Is this what you want?
If you want to avoid plotting the central point of each step, the easiest way is set x to:
x = -5.5:1:4.5
This is the code I used:
f(x) = floor(x + 1/2)
x = -5.5:1:4.5
y = f.(x)
plot(x[1:2], [y[1], y[1]], label=L"f(x) = \lfloor x + 1/2 \rfloor", legend=:bottomleft,legend_foreground_color=:white,
legend_font_color=:blue, color=:blue, showaxis=false, tickfontcolor=:white)
# axis
hline!((0,0), color=:black, label="")
vline!((0,0), color=:black, label="")
# Scale values
for i in x
if i!= 0
annotate!(i,-0.2, (i, 7))
end
end
for i in y
if i != 0
annotate!(-.2, i, (i, 7))
end
end
annotate!(-.2, -.2, ("0", 7))
# Plot function
for i in 2:length(x)-1
plot!(x[i:i+1], [y[i], y[i]], label="", color=:blue, lw=2)
end
Javier
1 Like
I actually tried this
using Plots, LaTeXStrings, Plots.PlotMeasures
gr()
f(x) = floor(x + 1/2)
x = -5:.5:4
y = f.(x)
plot(x[1:2], [y[1], y[1]], label=L"f(x) = \lfloor x \rfloor", legend=:topleft,legend_foreground_color=:white, legend_font_color=:blue3, color=:blue3, showaxis=false, tickfontcolor=:white)
# axis and
hline!((0,0), color=:black, label="")
vline!((0,0), color=:black, label="")
for i in x
if i!= 0
annotate!(i,-0.2, (i, 7))
end
end
for i in y
if i != 0
annotate!(-.2, i, (i, 7))
end
end
for i in 2:length(x)-1
plot!(x[i:i+1], [y[i], y[i]], label="", color=:blue3, lw=2)
scatter!(x[i], y[i], marker=:circle, markersize=8, label="")
end
and it returns error:
LoadError: Cannot convert Float64 to series data for plotting
seems the scatter function is problematic for using float or decimal value.
Then I try your code:
using Plots, LaTeXStrings, Plots.PlotMeasures
pyplot()
f(x) = floor(x + 1/2)
x = -5.5:1:4.5
y = f.(x)
plot(x[1:2], [y[1], y[1]], label=L"f(x) = \lfloor x + 1/2 \rfloor", legend=:bottomleft,legend_foreground_color=:white,
legend_font_color=:blue, color=:blue, showaxis=false, tickfontcolor=:white)
# axis
hline!((0,0), color=:black, label="")
vline!((0,0), color=:black, label="")
# Scale values
for i in x
if i!= 0
annotate!(i,-0.2, (i, 7))
end
end
for i in y
if i != 0
annotate!(-.2, i, (i, 7))
end
end
annotate!(-.2, -.2, ("0", 7))
# Plot function
for i in 2:length(x)-1
plot!(x[i:i+1], [y[i], y[i]], label="", color=:blue, lw=2)
end
the GUI window is not showing up, weird, but the REPL shows it is done…
scatter expects a vector of numbers, you need scatter!([x[i]], [y[i]]) although at that point you might as well just pull it out of the loop and write scatter!(x[2:length(x)-1], y[2:length(x)-1]) (which will also make the plot window show up as per my response in the other thread)
1 Like
I just read your reply more carefully and after lots of trial it works with this code:
using Plots; gr()
f(x) = floor(x + 1/2)
x = -5.5:1:4.5
y = f.(x)
plot(x[1:2], [y[1], y[1]], label=L"f(x) = \lfloor x + 1/2 \rfloor", legend=:bottomleft,legend_foreground_color=:white, legend_font_color=:blue, color=:blue, showaxis=false, tickfontcolor=:white)
# axis and
hline!((0,0), color=:black, label="")
vline!((0,0), color=:black, label="")
for i in x
if i!= 0
annotate!(i,-0.2, (i, 7))
end
end
for i in y
if i != 0
annotate!(-.2, i, (i, 7))
end
end
annotate!(-.2, -.2, ("0", 7))
for i in 2:length(x)-1
plot!(x[i:i+1], [y[i], y[i]], label="", color=:blue, lw=2)
end
scatter!(x[1:end-1], y[1:end-1], markersize=3, markercolor=:blue, label="")
scatter!(x[2:end], y[1:end-1], markersize=3, markercolor=:white, label="")