how to see what's wrong with a self written function?
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 <casperyc at 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
--
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