A C++ Math library which offers basic mathematical functions of trigonometry, exponentiation, rounding etc.
Questions tagged [cmath]
263 questions
104
votes
4 answers
When do I use fabs and when is it sufficient to use std::abs?
I assume that abs and fabs are behaving different when using math.h. But when I use just cmath and std::abs, do I have to use std::fabs or fabs? Or isn't this defined?
math
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70
votes
1 answer
What is 1LL or 2LL in C and C++?
I was looking at some of the solutions in Google Code Jam and some people used this things that I had never seen before. For example,
2LL*r+1LL
What does 2LL and 1LL mean?
Their includes look like this:
#include
#include…
fersarr
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69
votes
3 answers
Constexpr Math Functions
So noticed from this page that none of the math functions in c++11 seems to make use of constexpr, whereas I believe all of them could be. So that leaves me with two questions, one is why did they choose not to make the functions constexpr. And two…
aaronman
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67
votes
4 answers
Ambiguous overload call to abs(double)
I have the following C++ code:
#include
#include // per http://www.cplusplus.com/reference/clibrary/cmath/abs/
// snip ...
if ( (loan_balance < 0) && (abs(loan_balance) > loan_payment) ) {
...
}
and make blows up…
some_man
54
votes
7 answers
What is the correct way to obtain (-1)^n?
Many algorithms require to compute (-1)^n (both integer), usually as a factor in a series. That is, a factor that is -1 for odd n and 1 for even n. In a C++ environment, one often sees:
#include
#include
int main(){
int n = 13;
…
alfC
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52
votes
2 answers
Why is pow(int, int) so slow?
I've been working on a few project Euler exercises to improve my knowledge of C++.
I've written the following function:
int a = 0,b = 0,c = 0;
for (a = 1; a <= SUMTOTAL; a++)
{
for (b = a+1; b <= SUMTOTAL-a; b++)
{
c =…
Fang
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42
votes
3 answers
What's the difference between abs and fabs?
I checked the difference between abs and fabs on python here
As I understand there are some difference regarding the speed and the passed types, but my question related to native c++ on V.S.
Regarding the V.S.
I tried the following on Visual Studio…
Hazem Abdullah
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37
votes
7 answers
Definitions of sqrt, sin, cos, pow etc. in cmath
Are there any definitions of functions like sqrt(), sin(), cos(), tan(), log(), exp() (these from math.h/cmath) available ?
I just wanted to know how do they work.
Pythagoras of Samos
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34
votes
2 answers
abs vs std::abs, what does the reference say?
Beware, I am talking about ::abs(), not std::abs()
According to the cplusplus.com website, abs is supposed to behave differently for the stdlib.h C version, if you include
Here is an extract from the this page (which deals with ::abs, not…
Pascal T.
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29
votes
3 answers
Why are some functions in not in the std namespace?
I am developing a project which works with multiple arithmetic types. So I made a header, where the minimal requirements for a user defined arithmetic type are defined:
user_defined_arithmetic.h :
typedef double ArithmeticF; // The user chooses…
Martin Drozdik
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28
votes
5 answers
Rounding up and down a number C++
I'm trying to allow my program to round a number up and down respectively.
For example, if the number is 3.6, my program is suppose to round up the nearest number which is 4 and if the number is 3.4, it will be rounded down to 3.
I tried using the…
Bryan
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25
votes
3 answers
Template version of std::abs
Here lists the current overloads of std::abs in C++. I'm wondering why not just define the following template and let go all the ugly C-style overloads?
template inline
T abs(const T& v) { return v < 0 ? -v : v; }
Lingxi
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24
votes
3 answers
hides isnan in in C++14 / C++11?
I have here a small test app which uses isnan from :
#include
#include
int main()
{
double d = NAN;
std::cout << isnan(d) << '\n';
return 0;
}
Build and run under 3 different standards:
$ g++ -std=c++98…
Steve Lorimer
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22
votes
4 answers
Why is std::sin() and std::cos() slower than sin() and cos()?
Test code:
#include
#include
const int N = 4096;
const float PI = 3.1415926535897932384626;
float cosine[N][N];
float sine[N][N];
int main() {
printf("a\n");
for (int i = 0; i < N; i++) {
for (int j = 0; j < N;…
ornerylawn
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22
votes
5 answers
C/C++ fastest cmath log operation
I'm trying to calculate logab (and get a floating point back, not an integer). I was planning to do this as log(b)/log(a). Mathematically speaking, I can use any of the cmath log functions (base 2, e, or 10) to do this calculation; however, I will…
Nick
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