Question for maclaurian series

[harrya]

I have written this code for Maclaurian series. however, this is not getting executed. Kindly help

double ExpSeries(double x, int N)
{
//int acc = 1;
int N = 2;
float answer = 1;
float temp = 1;
int i;
for (i = 1; i <= N; i++)
{
temp = (temp*i) / i;
answer += temp;
return answer;
return temp;
}
}
int main()
{
std::cout << "the sum of the exponential series is " << ExpSeries(1.0, 2) << std::endl;
}

[keskiverto]

First, please use code tags <>, when posting code.

#include <iostream>

double ExpSeries( double x, int N ) // x is not used in the function
{
  //int acc = 1;
  int N = 2; // this local N hides the parameter N.
  float answer = 1; // these are float, x is double. Intentional?
  float temp = 1;
  int i;
  for (i = 1; i <= N; i++)
  {
    temp = (temp*i) / i;
    answer += temp;
    return answer; // you return from first iteration
    return temp; // this line is never executed
  }
}

int main()
{
  std::cout << "the sum of the exponential series is " << ExpSeries(1.0, 2) << std::endl;
}

Let me write a second program that does exactly the same as yours:

#include <iostream>

double foo()
{
  float temp = (1.0f * 1) / 1;
  float answer = 1.0f + temp;
  return answer; // answer is float. Function returns double
}

int main()
{
  std::cout << "the sum of the exponential series is " << foo() << std::endl;
}

I don't know what the Maclaurian series is, but I bet that it is something else than foo.

[harrya]

Maclaurian series - 1+ [x/1!]+ [x^2/2!]+ [x^3/3!]..............
I was trying to write this code where the next term is multiplied by x^n/n and then the sum is taken for all depending upon the value of n.

<
#include <iostream>

double ExpSeries( double x, int N ) // x is not used in the function
{
int N = 2; // this local N hides the parameter N - // What do you mean by this line, can you explain it further?
float answer = 1; // these are float, x is double. Intentional? // Yes
float temp = 1;
int i;
for (i = 1; i <= N; i++)
{
temp = (temp*i) / i;
answer += temp;
return answer; // you return from first iteration // how do i return both the values of temp and answer in the program?
return temp; // this line is never executed
}
}

int main()
{
std::cout << "the sum of the exponential series is " << ExpSeries(1.0, 2) << std::endl;
}
>

[lastchance]

@harrya,

Please study @Keskiverto's comments first. Then:
- remove the line int N = 2; completely; N IS SUPPLIED BY THE FUNCTION'S PARAMETER LIST - LOOK AT IT!
- remove the line return temp; completely; you DON'T NEED TO RETURN temp.
- move return answer; to after the loop;
- you should definitely use double, rather than float; there's nothing "intentional" about it; it's just silly here.

Your biggest mathematical error is
temp = (temp*i) / i;
which should be
temp = (temp*x) / i;

To get any sensible result, test with something considerably bigger than N=2 (e.g. 10 or above) and compare with std::exp(x), for which you will need the header <cmath>


A "Maclaurin series" is just a Taylor-Series expansion about x=0 (i.e., it's what you would most commonly think of as a power series in increasing powers of x).


PUT YOUR CODE IN CODE TAGS - it's the first item in the Format menu to the right of your text-entry box.

[keskiverto]

// this local N hides the parameter N - // What do you mean by this line, can you explain it further?

// these are float, x is double. Intentional? // Yes

// you return from first iteration // how do i return both the values of temp and answer in the program?

int snafu(
  int foo // this function has a variable that has name foo
 )
{
  int foo = 42; // this function has a variable that has name foo
  
  // if I now mention 'foo', do I mean 'foo' or 'foo'? They are two separate variables
  // The compiler assumes that I mean the 'foo' that has been
  // declared in the innermost scope
  // What scopes do you see in this code?
  return foo;
}

Your input data has type double.
Your function returns a double.
Why do you shrink intermediate values to float?
Why?


Why should the function return two values?
Does the "Maclaurin series" really produce a pair of values?
I thought that it is a sum; one value.

There are two ways for a function to return multiple values.
One is that it modifies caller's variables by reference.
The other is that it returns a data structure object that contains multiple values. For example, a tuple, a pair, a struct, or a class. (Cannot be a plain array.)