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 là où TRUE / FALSE est requis
De plus : Message d'avis :
In log(x) : production de NaN
This 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
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and provide commented, minimal, self-contained, reproducible code.
