Hi,
My name is Curtis and I'm a 1st year student in Biochemistry at the
University of Geneva. I need some help completing the code for my NEWTON
ALGORITHM. It is a bonus exercice to our autumn semester maths exam and we
can hand it in or not. Usually people copy and paste but I decided to sit
down and review theory and ask for help left right and center.
My problem is that I cannot get my function to give me the solution. Here
is my code:
## PRIMARY FUNCTION
f=function(x){
out=(2/(3))*exp(x^3)-(10)*log(x)
return(out)
}
## 1ST DERIVATIVE
fp=function(x){
out=(2)*(x^2)*exp(x^3)-(10/x)
return(out)
}
## 2ND DERIVATIVE
fpp=function(x){
out=(4)*(x)*exp(x^3)+(6)*(x^4)*exp(x^3)+(10/x^2)
return(out)
}
I am trying to find the "zero" of "fp",my 1st derivative,
with my newton
algorithm:
newbon=function(x0,epsi,f,fp){
## where "a" corresponds to x^n et
## "b" corresponds to x^n+1
## We are looking for x^n+1 such that f(x^n+1)=0
## NB: fp(a)*(a-b)=f(a) when f(b)=0
a=x0
b=(fp(a)*a-f(a))/fp(a)
while(abs(-fp(a)*(b-a))>epsi){
a=b
b=(fp(a)*a-f(a))/fp(a)
}
out=NULL
out=a
return(out)
}
I must admit that my algorithm was painfully congested and I've been having
headaches to get it to work. However, I always get the same error message:
Erreur dans while (abs(-fp(a) * (b - a)) > epsi) { :
valeur manquante là où TRUE / FALSE est requis
De plus : Message d'avis :
In log(x) : production de NaN
Please forgive the French; it is my study language. Quite frankly I don't
mind if I don't get the bonus marks, what is really important is that I
understand why it doesn't work and what condition is missing.
You're help would be kindly appreciated.
Curtis MOYO
[[alternative HTML version deleted]]
On 21.12.2011 22:43, Curtis Moyo wrote:> Hi, > > My name is Curtis and I'm a 1st year student in Biochemistry at the > University of Geneva. I need some help completing the code for my NEWTON > ALGORITHM. It is a bonus exercice to our autumn semester maths exam and we > can hand it in or not. Usually people copy and paste but I decided to sit > down and review theory and ask for help left right and center. > > My problem is that I cannot get my function to give me the solution. Here > is my code: > > ## PRIMARY FUNCTION > f=function(x){ > out=(2/(3))*exp(x^3)-(10)*log(x) > return(out) > } > ## 1ST DERIVATIVE > fp=function(x){ > out=(2)*(x^2)*exp(x^3)-(10/x) > return(out) > } > ## 2ND DERIVATIVE > fpp=function(x){ > out=(4)*(x)*exp(x^3)+(6)*(x^4)*exp(x^3)+(10/x^2) > return(out) > } > > I am trying to find the "zero" of "fp",my 1st derivative, with my newton > algorithm: > > newbon=function(x0,epsi,f,fp){ > > ## where "a" corresponds to x^n et > > ## "b" corresponds to x^n+1 > > ## We are looking for x^n+1 such that f(x^n+1)=0 > > ## NB: fp(a)*(a-b)=f(a) when f(b)=0 > > a=x0 > b=(fp(a)*a-f(a))/fp(a) > while(abs(-fp(a)*(b-a))>epsi){ > a=b > b=(fp(a)*a-f(a))/fp(a) > } > out=NULL > out=a > return(out) > } > > I must admit that my algorithm was painfully congested and I've been having > headaches to get it to work. However, I always get the same error message: > > Erreur dans while (abs(-fp(a) * (b - a))> epsi) { : > valeur manquante l? o? TRUE / FALSE est requis > De plus : Message d'avis : > In log(x) : production de NaNThis question (like all homework questions) is inappropriate on this mailing list and we usually do not give any answers in such cases! You should ask your instructor. She or he will certainly answer like this: "If you read that: log() produced NaN, hence was undefined. Now, you have only one function call for log, so think about when log(x) is undefined ..." Uwe Ligges> Please forgive the French; it is my study language. Quite frankly I don't > mind if I don't get the bonus marks, what is really important is that I > understand why it doesn't work and what condition is missing. > > You're help would be kindly appreciated. > > Curtis MOYO > > [[alternative HTML version deleted]] > > > > > ______________________________________________ > 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.
delongman wrote> > Hi, > > My name is Curtis and I'm a 1st year student in Biochemistry at the > University of Geneva. I need some help completing the code for my NEWTON > ALGORITHM. It is a bonus exercice to our autumn semester maths exam and we > can hand it in or not. Usually people copy and paste but I decided to sit > down and review theory and ask for help left right and center. > > My problem is that I cannot get my function to give me the solution. Here > is my code: > > ## PRIMARY FUNCTION > f=function(x){ > out=(2/(3))*exp(x^3)-(10)*log(x) > return(out) > } > ## 1ST DERIVATIVE > fp=function(x){ > out=(2)*(x^2)*exp(x^3)-(10/x) > return(out) > } > ## 2ND DERIVATIVE > fpp=function(x){ > out=(4)*(x)*exp(x^3)+(6)*(x^4)*exp(x^3)+(10/x^2) > return(out) > } > > I am trying to find the "zero" of "fp",my 1st derivative, with my newton > algorithm: > > newbon=function(x0,epsi,f,fp){ > > ## where "a" corresponds to x^n et > > ## "b" corresponds to x^n+1 > > ## We are looking for x^n+1 such that f(x^n+1)=0 > > ## NB: fp(a)*(a-b)=f(a) when f(b)=0 > > a=x0 > b=(fp(a)*a-f(a))/fp(a) > while(abs(-fp(a)*(b-a))>epsi){ > a=b > b=(fp(a)*a-f(a))/fp(a) > } > out=NULL > out=a > return(out) > } > > I must admit that my algorithm was painfully congested and I've been > having > headaches to get it to work. However, I always get the same error message: > > Erreur dans while (abs(-fp(a) * (b - a)) > epsi) { : > valeur manquante l? o? TRUE / FALSE est requis > De plus : Message d'avis : > In log(x) : production de NaN > > Please forgive the French; it is my study language. Quite frankly I don't > mind if I don't get the bonus marks, what is really important is that I > understand why it doesn't work and what condition is missing. > > You're help would be kindly appreciated. >As others have told you: no homework. But to give you some additional hints: 1. are you sure that your function has a solution for f(x)=0? 2. make your code readable: indent and use <- for assignment. 3. Try your newbon-function (shouldn't that be newton?) with this g <- function(x){ out <- (2/(3))*exp(x^2)-(20)*log(x) return(out) } gp <- function(x) { out <- (4/3)*exp(x) - 20/x return(out) } 4. do curve(f, <number>,<number>) and the same for g. The rest is up to you if you want to deserve a well-earned bonus. Berend -- View this message in context: http://r.789695.n4.nabble.com/NEWTON-ALGORITHM-tp4224558p4224816.html Sent from the R help mailing list archive at Nabble.com.
Berend Hasselman wrote> > ..... > > g <- function(x){ > out <- (2/(3))*exp(x^2)-(20)*log(x) > return(out) > } > > gp <- function(x) { > out <- (4/3)*exp(x) - 20/x > return(out) > } >function gp is incorrect. It should be gp <- function(x) { out <- (4/3)*x*exp(x^2) - 20/x return(out) } Berend -- View this message in context: http://r.789695.n4.nabble.com/NEWTON-ALGORITHM-tp4224558p4225321.html Sent from the R help mailing list archive at Nabble.com.
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