Re: [R] how to see what's wrong with a self written function?
Hi Petr Savicky, It is very interesting and a good way to plot, so that helps me to visualized the method, also easier to see what's wrong. The readline is new to me, and I should learn how to use it in the future. Thanks! casper -- View this message in context: http://r.789695.n4.nabble.com/how-to-see-what-s-wrong-with-a-self-written-function-tp3159528p3168994.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.
Re: [R] how to see what's wrong with a self written function?
On Tue, Dec 21, 2010 at 11:39:31AM -0800, casperyc 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 x0, 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?
The previous replies imply that at some point, your code evaluates the
function outside the required interval. The reason for this may be seen
using graphics. If you add plot commands to your code, for example
regulafalsi=function(f,x0,x1){
z - seq(x0, x1, lenth=1000)
plot(z, f(z), type=l)
abline(h=0)
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))
lines(c(x0, x[i-1]), c(f(x0), f(x[i-1])), col=2)
} else {
x[i]=x[i-1]-f(x[i-1])*(x[i-1]-x[i-2])/(f(x[i-1])-f(x[i-2]))
lines(c(x[i-2], x[i-1]), c(f(x[i-2]), f(x[i-1])),
col=2)
}
points(x[i], 0)
aux - readline(press Enter to continue)
}
x[i]
}
regulafalsi(function(x) x^(1/2)+3*log(x)-5,1,10)
regulafalsi(function(x) x^(1/2)+3*log(x)-5,1,100)
then it may be seen that for [1, 10], we get convergence, while for [1, 100]
the secant line in the second iteration does not intersect x-axis inside the
required interval.
Petr Savicky.
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[R] how to see what's wrong with a self written function?
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 x0, 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.
Re: [R] how to see what's wrong with a self written function?
On 21/12/2010 2:39 PM, casperyc 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 x0, 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?
The easiest is to just use regular old-fashioned debugging methods, i.e.
insert print() or cat() statements into your function. You could also
try debug(regulafalsi) and single step through it to see where things go
wrong. (An obvious guess is that one of the values being passed to f is
negative, but you'll have to figure out why that happened and what to do
about it.)
Duncan Murdoch
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] 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] 100.0 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 x0, 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?
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