finding cube root in C++?

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Strange things happen when i try to find the cube root of a number.

The following code returns me undefined. In cmd : -1.#IND

cout<<pow(( double )(20.0*(-3.2) + 30.0),( double )1/3)

While this one works perfectly fine. In cmd : 4.93242414866094

cout<<pow(( double )(20.0*4.5 + 30.0),( double )1/3)

From mathematical way it must work since we can have the cube root from a negative number. Pow is from Visual C++ 2010 math.h library. Any ideas?

Find cubic root of a number, If (mid*mid*mid)<n set start=mid. Below is the implementation of above idea. C++​; Java; Python3; C#; PHP. C++. Find Cube Root of Any Number In C - To find cube root of any number we need to find 0.3 power of any number. For example if you need to find cube root of 27 then calculate 0.3 power of 27, result is 3.

The power 1/3 is a special case. In general, non-integral powers of negative numbers are complex. It wouldn't be practical for pow to check for special cases like integer roots, and besides, 1/3 as a double is not exactly 1/3!

I don't know about the visual C++ pow, but my man page says under errors:

EDOM The argument x is negative and y is not an integral value. This would result in a complex number.

You'll have to use a more specialized cube root function if you want cube roots of negative numbers - or cut corners and take absolute value, then take cube root, then multiply the sign back on.

Note that depending on context, a negative number x to the 1/3 power is not necessarily the negative cube root you're expecting. It could just as easily be the first complex root, x^(1/3) * e^(pi*i/3). This is the convention mathematica uses; it's also reasonable to just say it's undefined.

Cube Root Program In C, Cube Root Program In C - Finding that a given number is even or odd, is a classic C program. We shall learn the use of conditional statement if-else in C. The main steps of our algorithm for calculating the cubic root of a number n are: Initialize start = 0 and end = n Calculate mid = (start + end)/2 Check if the absolute value of (n – mid*mid*mid) < e.

While (-1)^3 = -1, you can't simply take a rational power of a negative number and expect a real response. This is because there are other solutions to this rational exponent that are imaginary in nature. http://www.wolframalpha.com/input/?i=x^(1/3),+x+from+-5+to+0

Similarily, plot x^x. For x = -1/3, this should have a solution. However, this function is deemed undefined in R for x < 0.

Therefore, don't expect math.h to do magic that would make it inefficient, just change the signs yourself.

How can I obtain the cube root in C++?, sqrt stands for "square root", and "square root" means raising to the power of 1/2 . There is no such thing as "square root with root 2", or "square  C library function - sqrt() - The C library function double sqrt(double x) returns the square root of x.

Guess you gotta take the negative out and put it in afterwards. You can have a wrapper do this for you if you really want to.

function yourPow(double x, double y)
{
    if (x < 0)
        return -1.0 * pow(-1.0*x, y);
    else
        return pow(x, y);
}

Find Cube Root of Any Number Program in C - C Programs, For example if you need to find cube root of 27 then calculate 1/3 power of 27, result is 3. Find Cube Root of Any Number Program in C. #include<stdio.h> #​include  It uses Newton-Raphson to find a cube root. Sometime Newton -Raphson gets stuck, if the root is very close to 0 then the derivative can get large and it can oscillate. So I've clamped and forced it to restart if that happens. If you need more accuracy you can change the FLT_EPSILONs.

Don't cast to double by using (double), use a double numeric constant instead:

double thingToCubeRoot = -20.*3.2+30;
cout<< thingToCubeRoot/fabs(thingToCubeRoot) * pow( fabs(thingToCubeRoot), 1./3. );

Should do the trick!

Also: don't include <math.h> in C++ projects, but use <cmath> instead.

Alternatively, use pow from the <complex> header for the reasons stated by buddhabrot

[Solved] Finding cube root of a number using pow function in C , Using float variables with pow is pointless. Try. Hide Copy Code. #include <stdio.​h> #include <math.h> int main() { double a, b; // pow takes  The C language can be used for mathematical operations, ranging from additions and subtractions to square roots and cube roots, along with other polynomial powers that can be created through C programming. To find the square root of a number, you can customize the C script to code the logic by using the sqrt function.

C programming tutorial to find cubic root, This is a simple c programming code for cubic root.Here i have used cbrt function to find cubic Duration: 3:09 Posted: Jan 30, 2016 To find cube root of any number we need to find 0.3 power of any number. For example if you need to find cube root of 27 then calculate 0.3 power of 27, result is 3. And one another method for this program is use cbrt () function it is pre-defined in math.h header file. Cube Root program in C++

C Program to find Cube Root of a Number, Sources Code ********** Link :- https://goo.gl/nZ8PzR.Duration: 4:31 Posted: Jul 30, 2018 Find the next number in your cube root solution. Find the next digit of your solution by selecting what you can multiply by the divisor, 1200-something, to then subtract from the remainder of 2000. This can only be 1, since 2 times 1200 would be 2400, which is greater than 2000. Write the number 1 in the next space above the radical sign.

C++ Program to Find Cube Root of Number, In the first example we will use std::pow function to find the cube root of a given number. C++. Today we will learn the Babylonian method to find the square root using C++. This method basically originates from the newton-raphson method. We all know what a square root of a number is and this method is an olden time approach to computing just that.

Comments
  • i didn't knew this. since there is no n-th root function in cmath i've improvised.
  • Funny that this accepted answer precisely explains why the "workaround" will not work !
  • well, it's a function which must have values both negative and positive. I'll put a if for this.
  • Isn't this known as performing a cut along the line x<0?
  • @DavidHeffernan, yes, it does, according to mathworld.wolfram.com/CubeRoot.html we have "However, extension of the cube root into the complex plane gives a branch cut along the negative real axis for the principal value of the cube root".
  • Er, double cast was fine, this fails too because it sends the same values to pow; @birryree has the answer
  • It has been a while but (sign==true)?return x:return -x; seriously? Is this valid C/++? Why not go with return sign ? x : -x;? The same for x>=0?sign=true:sign=false; -> sign = (x >= 0);.
  • (sign==true)?return x:return -x; is a syntax error. Nobody's suggestions are cleaner and correct.
  • The focus of this thread is the algorithm and not c++. I offered a method that works and anybody should understand what I meant. You also understood it, didn't you?
  • well there is no rt(x,3) in c++
  • @ilcredo Mine was a math advice
  • your curt algorithm is wrong. It should be (2 * b + x / b / b) / 3
  • This is a good suggestion as it improves runtime for small numbers. x = 12 from 26 to 5 iterations. However, for big numbers: x = 7e+122 from 161 to 235 iterations. Iterations were equal at x = 7e+30. Thanks.
  • for a large number X try (i) passing 1 / X into the routine and do 1 / result; (ii) dividing by a known cube number below X and multiplying by the cube root at the end