Newton-Raphson algorithm

Question

consider the Newton-Raphson algorithm for calculating the roots of the equation f(x)=0 with (0.5, 1 , 2 , 3.4556) for each initial x.

f(X)=X 4-12X 3+47x 2-60X I made the same code as the algorithm, but this not finding the roots, someone can help me?

#include <stdio.h>

float Abs( float x ){

  return x>=0? x:-x;
};

int main(){
  float xini = 0, xnovo , Fxnovo, Fdxnovo , E ;     
  int k = 0;

  printf( "Digite o x inicial: " );
  scanf( "%f", &xnovo );
  printf( "Digite a precisao: " );
  scanf( "%f", &E );

  do{

    xini = xnovo;
    Fxnovo = ( xini * xini * xini * xini ) - 12 * (xini * xini * xini) + 47*(xini * xini) - 60 * xini; //inserir sua função principal aqui
    Fdxnovo = 4. * ( xini * xini * xini) - 36. * (xini * xini ) + 94 * xini - 60; //inserir a derivada da função principal aqui
    xnovo = xini - ( Fxnovo / Fdxnovo );
    k += 1;
    printf( "\niteracao = %d", k );
    printf( "\nxini = %f\nxnovo = %f", xini, xnovo, Fxnovo, Fdxnovo );

  } while(Abs(Fxnovo) > E);

  printf( "\n\nxnovo - xini = %f\n", xnovo -(xini) );
  printf( "A solucao final e: %f\n", xnovo );

  return 0;
}

Answer 1

The error is in the definition of Abs. Currently, Abs(4) will return -4. So just find the first f(x) positive that will come out of the loop.

The correction is as follows:

float Abs( float x ){
  return x >=0? x: -x;
}