Here is what I get when I have:
options(error=utils::recover)
I always run with the option so that on an error, I get dumped in the
browser to see what is happening. It appears that 'i == 3' when the
error occurs and you can also see the values of 'x':
> regulafalsi=function(f,x0,x1){
+ x=c()
+ x[1]=x1
+ i=1
+ while ( f(x[i])!=0 ) {
+ i=i+1
+ if (i==2) {
+ x[2]=x[1]-f(x[1])*(x[1]-x0)/(f(x[1])-f(x0))
+ } else {
+
x[i]=x[i-1]-f(x[i-1])*(x[i-1]-x[i-2])/(f(x[i-1])-f(x[i-2]))
+ }
+ }
+ x[i]
+ }
> regulafalsi(function(x) x^(1/2)+3*log(x)-5,10,1)
[1] 2.978429
> regulafalsi(function(x) x^(1/2)+3*log(x)-5,1,100)
Error in while (f(x[i]) != 0) { : missing value where TRUE/FALSE needed
In addition: Warning message:
In log(x) : NaNs produced
Enter a frame number, or 0 to exit
1: regulafalsi(function(x) x^(1/2) + 3 * log(x) - 5, 1, 100)
Selection: 1
Called from: top level
Browse[1]> i
[1] 3
Browse[1]> x
[1] 100.00000 18.35661 -42.22301
Browse[1]>
On Tue, Dec 21, 2010 at 2:39 PM, casperyc <caspe...@hotmail.co.uk> wrote:
>
> Hi all,
>
> I am writing a simple function to implement regularfalsi (secant) method.
>
> ###################################################
> regulafalsi=function(f,x0,x1){
> x=c()
> x[1]=x1
> i=1
> while ( f(x[i])!=0 ) {
> i=i+1
> if (i==2) {
> x[2]=x[1]-f(x[1])*(x[1]-x0)/(f(x[1])-f(x0))
> } else {
>
> x[i]=x[i-1]-f(x[i-1])*(x[i-1]-x[i-2])/(f(x[i-1])-f(x[i-2]))
> }
> }
> x[i]
> }
> ###################################################
>
> These work fine,
> regulafalsi(function(x) x^(1/2)+3*log(x)-5,1,10)
> regulafalsi(function(x) x^(1/2)+3*log(x)-5,10,1)
>
> For all x>0, the function is strictly increasing.
>
> Then
>
> regulafalsi(function(x) x^(1/2)+3*log(x)-5,1,100)
>
> Error in while (f(x[i]) != 0) { : missing value where TRUE/FALSE needed
> In addition: Warning message:
> In log(x) : NaNs produced
>
> I dont know what happened there, is there a way to find the value for
> f(x[i])
> that R can't determine TRUE/FALSE?
>
> Thanks!
>
> casper
> --
> View this message in context:
> http://r.789695.n4.nabble.com/how-to-see-what-s-wrong-with-a-self-written-function-tp3159528p3159528.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@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.
>
--
Jim Holtman
Data Munger Guru
What is the problem that you are trying to solve?
______________________________________________
R-help@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.
