## the batman equation

HardOCP has an image with an equation which apparently draws the Batman logo.

$((\frac{x}{7})^2 \cdot \sqrt{\frac{||x|-3|}{(|x|-3)}}+ (\frac{y}{3})^2 \cdot \sqrt{\frac{|y+3 \cdot \frac{\sqrt{33}}{7}|}{y+3 \cdot \frac{\sqrt{33}}{7}}}-1) \cdot (|\frac{x}{2}|-((3 \cdot \frac{\sqrt{33}-7)}{112}) \cdot x^2-3+\sqrt{1-(||x|-2|-1)^2}-y) \cdot (9 \cdot \sqrt{\frac{|(|x|-1) \cdot (|x|-0.75)|}{((1-|x|)*(|x|-0.75))}}-8 \cdot |x|-y) \cdot (3 \cdot |x|+0.75 \cdot \sqrt{\frac{|(|x|-0.75) \cdot (|x|-0.5)|}{((0.75-|x|) \cdot (|x|-0.5))}}-y) \cdot (2.25 \cdot \sqrt{\frac{|(x-0.5) \cdot (x+0.5)|}{((0.5-x) \cdot (0.5+x))}}-y) \cdot (\frac{6 \cdot \sqrt{10}}{7}+(1.5-0.5 \cdot |x|) \cdot \sqrt{\frac{||x|-1|}{|x|-1}}-(\frac{6 \cdot \sqrt{10}}{14}) \cdot \sqrt{4-(|x|-1)^2}-y) =0$

This function is very delightful for drawing such a graph, but write it down in latex is very tedious.

As a product of factors is 0 if and only if any one of them is 0, multiplying these six factors puts the curves together. This graph is no more than the combination of six curves.

All these six curves are very simple, for instance, the first factor is the ellipse $(\frac{x}{7})^2 + (\frac{y}{3})^2 = 1$ , in the region where |x|>3 and y>-3 $\sqrt{33}$ /7; the region were restricted by $\sqrt{\frac{||x|-3|}{(|x|-3)}}$ and $\sqrt{\frac{|y+3 \cdot \frac{\sqrt{33}}{7}|}{y+3 \cdot \frac{\sqrt{33}}{7}}}$

Here's what I got from the equation using ggplot2...

?View Code RSPLUS
 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58    require(ggplot2)   f1 <- function(x) { y1 <- 3*sqrt(1-(x/7)^2) y2 <- -3*sqrt(1-(x/7)^2) y <- c(y1,y2) d <- data.frame(x=x,y=y) d <- d[d\$y > -3*sqrt(33)/7,] return(d) }   x1 <- c(seq(3, 7, 0.001), seq(-7, -3, 0.001)) d1 <- f1(x1) p1 <- ggplot(d1,aes(x,y)) + geom_point(color="red")   x2 <- seq(-4,4, 0.001) y2 <- abs(x2/2)-(3*sqrt(33)-7)*x2^2/112-3 + sqrt(1-(abs(abs(x2)-2)-1)^2)   #only work with ggplot2 <= 0.8.9 #p2 <- p1 + geom_point(aes(x=x2,y=y2), color="yellow")   # in ggplot2 0.9.0, should be: d2 <- data.frame(x2=x2, y2=y2) p2 <- p1 + geom_point(data=d2, aes(x=x2,y=y2), color="yellow")       x3 <- c(seq(0.75,1,0.001), seq(-1,-0.75,0.001)) y3 <- 9-8*abs(x3) #p3 <- p2+geom_point(aes(x=x3,y=y3), color="green") d3 <- data.frame(x3=x3, y3=y3) p3 <- p2+geom_point(data=d3, aes(x=x3,y=y3), color="green")     x4 <- c(seq(0.5,0.75,0.001), seq(-0.75,-0.5,0.001)) y4 <- 3*abs(x4)+0.75 #p4 <- p3+geom_point(aes(x=x4,y=y4), color="steelblue") d4 <- data.frame(x4=x4,y4=y4) p4 <- p3+geom_point(data=d4, aes(x=x4,y=y4), color="steelblue")     x5 <- seq(-0.5,0.5,0.001) y5 <- rep(2.25,length(x5)) #p5 <- p4+geom_point(aes(x=x5,y=y5)) d5 <- data.frame(x5=x5,y5=y5) p5 <- p4+geom_point(data=d5, aes(x=x5,y=y5))   x6 <- c(seq(-3,-1,0.001), seq(1,3,0.001)) y6 <- 6 * sqrt(10)/7 + (1.5 - 0.5 * abs(x6)) * sqrt(abs(abs(x6)-1)/(abs(x6)-1)) - 6 * sqrt(10) * sqrt(4-(abs(x6)-1)^2)/14 #p6 <- p5+geom_point(aes(x=x6,y=y6), colour="blue") d6 <- data.frame(x6=x6,y6=y6) p6 <- p5+geom_point(data=d6,aes(x=x6,y=y6), colour="blue")   p <- p6+theme_bw() print(p)

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1. When I (mindlessly) run the above R script, I get the Console error output:
> print(p)
Error in data.frame(..., check.names = FALSE) :
arguments imply differing number of rows: 8001, 14002

and a blank plot canvass.

I was able to narrow this error down to p2:
> p2
Error in data.frame(..., check.names = FALSE) :
arguments imply differing number of rows: 8001, 14002

p1 plots the 2 base ellipse components (outer wings) correctly.

you did not run the following command correctly.

p2 < - p1 + geom_point(aes(x=x2,y=y2), color="yellow")


Your error is due to the typo. You key in x or y instead of x2 or y2, and geom_point will parse it according to the dataset provided by p1.

> dim(d1)
[1] 14002     2
> length(x2)
[1] 8001
> length(y2)
[1] 8001


2. Berend Hasselman

I am trying to run the batman curve with R2.14.2 and ggplot2 0.9.0
I am now getting the same error message as Rudy Rooz reported.
I did not get that error message before.

What has changed with ggplot? Any idea how to repair this?

corrected, now work with ggplot2 0.9.0.