function curve() swap axes
On 05/07/2012 8:34 AM, Boudewijn Verkooijen wrote:
Dear all, I'm using the curve() function to plot discharge Q against water depth a. However, I would like to have a graph of water depth a plotted against discharge Q. How can this be done?
curve() is designed for plotting y vs x where y is a function of x, so I think you need to do it yourself. Simply compute a vector of "a" values using seq(), compute the corresponding Q values using your formula, and then use plot(Q, a, type="l") You can add the lwd and other arguments too if you like. Duncan Murdoch
Minimal working example:
S0 = 0.004
n = 0.04
tanalpha = 1.4/1.5
par(mar = c(5,5,1,1)) # b, l, t, r
curve((sqrt(S0)/n)*(0.035+(0.7+(x-0.1)/tanalpha)*(x-0.1))*((0.035+(0.7+(x-0.1)/tanalpha)*(x-0.1))/(2*sqrt((0.7/2)^2+0.1^2)+2*sqrt((x-0.1)^2+((x-0.1)/tanalpha)^2)))^(2/3),0.1,1.55,
lwd = 3, col = "royalblue4", ann = F, axes = T)
title(xlab = parse(text='a~bgroup("[", m, "]")'))
title(ylab = parse(text='Q~bgroup("[", m^3/s, "]")'))
box()
I tried to find the inverse function, but that doesn't seem to exist.
Thank you for support,
Boudewijn
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