R help - Apr 2012 - Simple Problem: Plotting mathematical functions

Hey there,
I want to plot 5 parabola functions, which happen to be 
f(x) = 0.25x? + 6,47x -32.6	
g(x)=0.99x? -6x -195	
j(x)= 0.77x? +14x -495		
k(x)=0.001x? + 65x -785		
l(x) = 0.9x? -2x -636 

in the same graph. Sadly I even do not really understand how to plot just
one graph...
I found this code in the Internet, which plots a cos-function:
>x <- seq( -10, 10, length = 1000)
>plot(x, *sin(x)*, xlab="x-values", ylab="f(x)",
type="l")
>lines(x, cos(x), lty=3)
>title( "Trigonometric functions", "sin(x) and cos(x)")
If I replace the sin(x) thing (bold) with one of my functions, it doesn't
work and reports an unwanted character.

Can somebody help me with that?

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Hi, 

At the moment I am studying R at school. 
But I found this site very useful to explain the plot functions to me: 

http://www.harding.edu/fmccown/r/ 

Maybe that can help you too? 


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Okay, i got this far:
f <- function(x) 0.25*x^2 + 6.47*x -32.6	
g <- function(x) 0.99*x^2 -6*x -195		
h <- function(x) 0.77*x^2 +14*x -495			
j <- function(x) 0.001*x^2 + 65*x -785		
k <- function(x) 0.9*x^2 -2*x -636 
plot(x, f(x), xlab="Elemente in der Reihung", ylab="Indexwert des
Sortieraufwands"), type="l") 
// lines(x, g(x), lty=3) //Not sure if it works, but this is irrelevant atm.

As soon as R does the plot command, he states that x is an object he can't
find. 
So i propably have to do something like x <- XXXXXXXXXX. What do I insert
for the XXXXXXXXX to make it have the values - say - from 15 to 10000?

Thanks again.

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It seems that your first problem is syntax:

2x

will thrown an error, while

2*x

won't.

Google around for a good intro tutorial (there's the main one you can
access by typing help.start() and it's quite good) and these sorts of
things will be explained.

You might also want to use the curve function (type ?curve at the
prompt for details)

e.g.,

curve(x^2, from = 0, to = 5)

plots x^2 from x = 0 to x = 5 and handles axes nicely.

Michael

On Thu, Apr 12, 2012 at 2:29 PM, Aye <muudle at hotmail.de>
wrote:
> Hey there,
> I want to plot 5 parabola functions, which happen to be
> f(x) = 0.25x? + 6,47x -32.6
> g(x)=0.99x? -6x -195
> j(x)= 0.77x? +14x -495
> k(x)=0.001x? + 65x -785
> l(x) = 0.9x? -2x -636
>
> in the same graph. Sadly I even do not really understand how to plot just
> one graph...
> I found this code in the Internet, which plots a cos-function:
>
>>x <- seq( -10, 10, length = 1000)
>>plot(x, *sin(x)*, xlab="x-values", ylab="f(x)",
type="l")
>>lines(x, cos(x), lty=3)
>>title( "Trigonometric functions", "sin(x) and
cos(x)")
>
> If I replace the sin(x) thing (bold) with one of my functions, it
doesn't
> work and reports an unwanted character.
>
> Can somebody help me with that?
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/Simple-Problem-Plotting-mathematical-functions-tp4552668p4552668.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Hi, 

you can use the curve() function for this. It is dedicated to plotting
functions. 

Here is an example

# turn your functions into r functions
f <- function(x) 0.25 * x^2 + 6.47 * x -32.6	
g <- function(x) 0.99*x^2 -6*x -195	
j <- function(x) 0.77*x^2 + 14*x -495		
k <- function(x) 0.001*x^2 + 65*x -785		
l <- function(x) 0.9*x^2 -2*x -636 

# plot f and g
curve(f, from=0, to=100, lty=1)
curve(g, add=TRUE, lty=2)


In this example, the parameters 'from' and 'to' define the
domain over wich
all functions will be evaluated. The parameter add=TRUE is used to add 
the second function to the previous plot. 

HTH

Matthieu

Matthieu Dubois 
Post-doctoral fellow, 
Psychology Department, Univerist? Libre de Bruxelles