Plotting a function curve in R with 2 or more variables

Question

How can I draw a curve for a function like vpd = function(k,D){exp(-k*D)} in R?

I want a plot of D vs vpd(0:1) assuming k is constant.

The only question I could find was How to plot a function curve in R . I've tried both of:

plot.function(vpd, from=0, to=1, n=101)

curve(vpd, from=0, to=1, n=101, add=FALSE, type = "l")

but only get

Error in -k * D : 'D' is missing

UPDATE: solved it!

vpd <- function(D,k=0.05){exp(-k*D)} # D is the x axis 
plot(vpd, from=1, to=100, ylim=0:1)

If you really want "a plot of D vs vpd(0:1) assuming k is constant (=0.05)", then that's not a 2D function plot, it's one single contour line of constant k(=0.05) on a 2D plot (please fix your title). Also, do you want a function that automatically generates a sensible range of (k,D) to show the interesting parts of the plot, or do you want to manually supply the range of k? — smci
– smci, Commented Apr 13, 2019 at 1:08
Also if you want to plot D vs vpd=0:1, then really you're exploring the reverse-function D = -log(vpd) / k — smci
– smci, Commented Apr 13, 2019 at 1:52

CL. · Accepted Answer · 2015-07-21 17:29:27Z

2

While Mamoun Benghezal's answer works for functions you define yourself, there may be cases where you want to plot a predefined function that expects more than 1 parameter. In this case, currying is a solution:

library(functional)

k <- 0.05

vpd <- function(k,D){exp(-k*D)}
vpd_given_k <- Curry(vpd, k = 0.05)

curve(vpd_given_k, ylim = c(0, 1),
      from = 1, to = 100, 
      xlab = "D", ylab = paste("vpd | k = ", k))

edited Jul 21, 2015 at 17:29

answered Jul 10, 2015 at 11:56

CL.

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8 Comments

Josh J Over a year ago

That nearly does it. The y-axis is right but I want the x-axis to be the length of D i.e. if D is between 0 and 20 that should be the scale on the axis rather than 0 to 1.

CL. Over a year ago

I am not entirely sure if I understand your comment because D is just a value and not a range. But I edited the answer such that the maximum of the x-axis is always D.

Gregor Thomas Over a year ago

From the question, I think OP is hoping to plot against D and hold k constant. Of course, since D and k are interchangeable in this equation that's really just a matter of labeling.

CL. Over a year ago

The question is a little bit mysterious - what does plot "D vs vpd(0:1)" mean? Only "plot vdp vs D" makes sense for me; and this is what you also suggest. However, I don't understand the OP's comment if this is true. @user3725599 can you clarify how the final plot should look like?

Josh J Over a year ago

Fixed it. Sorry for being vague. vpd <- function(D,k=0.05){exp(-k*D)} # D is the x axis plot(vpd, from=1, to=100, ylim=0:1)

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