R help - Jun 2011 - Trouble with compound functions---differential equations

Hi all,
My apologies if this message is incredibly inept but I am very new to both
computer programming and to R.

I am working with the odesolve add-on and have the following function
defined

RVF_Single <- function(t, x, p)
within the script I also have the following functions defined:

T1<-function(t) {T1<-27.5-12.5*cos(2*pi*t/365)}
and

B1<-function(T1,t) {B1<-dnorm(T1(t),mean=22.5,sd=3.3)}



When the script is run it doesn't return an error message but the graphs
returned are "wrong". When I input "plot(T1,0,3650)" it
returns the plot of
T1 as expected---a series of waves between 15 and 40, BUT when I input
"plot(B1,0,3650)" I get an error message of "Error in 2 * pi * t
: 't' is
missing".




Can anyone advise as to why t registers for function T1 but disappears for
function B1?


Thank you,


Aimee

ps: If it's relevant I'm using R64 (R 2.11.1) on a Mac

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On 16/06/11 11:07, Aimee Jones wrote:
> Hi all,
> My apologies if this message is incredibly inept but I am very new to both
> computer programming and to R.
>
> I am working with the odesolve add-on and have the following function
> defined
>
> RVF_Single<- function(t, x, p)
> within the script I also have the following functions defined:
>
> T1<-function(t) {T1<-27.5-12.5*cos(2*pi*t/365)}
> and
>
> B1<-function(T1,t) {B1<-dnorm(T1(t),mean=22.5,sd=3.3)}
     Actually your code should read:

T1<-function(t) {27.5-12.5*cos(2*pi*t/365)}

and

B1<-function(T1,t) {dnorm(T1(t),mean=22.5,sd=3.3)}

i.e. don't assign the value that you calculate in the code; this
is the value ***returned*** by the function.  What you is in effect
harmless here, but it is confusing and could cause problems in
other contexts.
> When the script is run it doesn't return an error message but the
graphs
> returned are "wrong". When I input "plot(T1,0,3650)" it
returns the plot of
> T1 as expected---a series of waves between 15 and 40, BUT when I input
> "plot(B1,0,3650)" I get an error message of "Error in 2 * pi
* t : 't' is
> missing".
>
> Can anyone advise as to why t registers for function T1 but disappears for
> function B1?
Well, T1() a function of ***t*** only (where t is the variable against which
you expect the values of T1() to be plotted.  Whereas, B1 is a function of
two variables T1 and t, which confuses things.

Note that by calling plot() in this way you are in fact calling 
plot.function()
which is in fact a wrapper for curve().  As has been discussed recently on
this list, the syntax for curve() is a bit delicate.

A workaround for your problem is:

     plot(function(t){B1(T1,t)},0,3650)

HTH

     cheers,

         Rolf Turner

Aimee Jones wrote:
> 
> Hi all,
> My apologies if this message is incredibly inept but I am very new to both
> computer programming and to R.
> 
> I am working with the odesolve add-on and have the following function
> defined
> 
> RVF_Single <- function(t, x, p)
> within the script I also have the following functions defined:
> 
> T1<-function(t) {T1<-27.5-12.5*cos(2*pi*t/365)}
> and
> 
> B1<-function(T1,t) {B1<-dnorm(T1(t),mean=22.5,sd=3.3)}
> 
> When the script is run it doesn't return an error message but the
graphs
> returned are "wrong". When I input "plot(T1,0,3650)" it
returns the plot
> of
> T1 as expected---a series of waves between 15 and 40, BUT when I input
> "plot(B1,0,3650)" I get an error message of "Error in 2 * pi
* t : 't' is
> missing".
> 
> Can anyone advise as to why t registers for function T1 but disappears for
> function B1?
> 
Because B1 is a function with 2 arguments.
plot calls B1 with 1 argument, which will be argument T1. So t is missing
since it hasn't received a value.

Redefine B1 as 

B1<-function(t) {B1<-dnorm(T1(t),mean=22.5,sd=3.3)}

and you will get your plot.

Berend


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