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

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