A newbie learning C here. Im currently practicing the concept of calling a recursive function between a range of inputs by utilizing a for loop and am running into a "segmentation fault : 11" error.

The attempted code and the error Im facing is posted below. Now I know this error is most likely is a result of me not being comfortable with the concept of recursion so any insight would help greatly! (Note: This is not for homework, just a challenge problem I would like to understand better.)

Here is the math function i am trying to apply recursion to along with its base case and its range of inputs to test.

g(2x)= 2g(x)/ 1 g^2(x)

• x in between the range of -1<= x <= 1;

• x in between the range of -1<= x <= 1;

• x incrementing 0.1

Base conditions:

• tolerance= 10^-6

  if (|x| < tolerance) return g(x)= x- x^3/6

Attempted Code

//Libraries
#include <iostream> 
#include <cmath>
using namespace std;

//Function Prototypes
float recFunc(float);

int main(int argc, char** argv) {
    //Call Recursive Function and Output Results

    //from negative 1 to z
    for (float x=-1.0; x<=0; x =0.1f){
        cout<<"X Value = "<<x<<" : g(2x) = "<<recFunc(x)<<endl;
    }

    //from 0 to 1
    for (float x=0; x<1.1; x =0.1f){
        cout<<"X Value = "<<x<<" : g(2x) = "<<recFunc(x)<<endl;
    }
    return 0;
}

float recFunc(float x){
    //Base condition
    float tol= 1e-6f;
    if(abs(x)< tol) return x-x*x*x/6;

    //Recursive Call
    float val= 2*(x-x*x*x/6)/1 (x-x*x*x/6)*(x-x*x*x/6);
    return 2*recFunc(val);
}

CodePudding user response：

The posted math formula is basically

g(2 * x) = F(g(x))

It can be rewritten as

g(x) = F(g( x / 2 ))

So, to fix recFunc, you have to:

1. Evaluate g at x/2. This is the recursive call to recFunc, but with x / 2 as argument. Assign the returned value to variable, like val.

2. Return F(val). Meaning, apply the posted formula to value calculated in the previous point.

CodePudding user response：

Here is the corrected code for the errors above in the recursive float function.

float recFunc(float x){
    //Base condition
    float tol= 1e-6f;
    if(abs(x)< tol) return x-x*x*x/6;

    //Recursive Call
    float val= recFunc(x/2);
    return 2*val/1 val*val;
}