cmath | 易学教程

Sin and Cos give unexpected results for well-known angles

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I am sure this is a really stupid question, but when I pass an angle of 180 degrees into c/c++'s cos() and sin() functions I appear to receive an incorrect value. I know that it should be: sin of 0.0547 and cos of 0.99 but I get sin of 3.5897934739308216e-009 and cos of -1.00000 My code is: double radians = DegreesToRadians( angle ); double cosValue = cos( radians ); double sinValue = sin( radians ); DegreesToRadians() is: double DegreesToRadians( double degrees ) { return degrees * PI / 180; } Thank you :) C/C++ provides sin(a) , cos(a) , tan(a) , etc. functions that require a parameter with

When do I use fabs and when is it sufficient to use std::abs?

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问题 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? 回答1: In C++, it's always sufficient to use std::abs ; it's overloaded for all the numerical types. In C, abs only works on integers, and you need fabs for floating point values. These are available in C++ (along with all of the C library), but there's no need to use them. 回答2: It's still okay to use fabs for double and float

Why are some functions in <cmath> not in the std namespace?

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问题 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 what type he // wants to use to represent a real number namespace arithmetic // and defines the functions related to that type { const ArithmeticF sin(const ArithmeticF& x); const ArithmeticF cos(const ArithmeticF& x); const ArithmeticF tan(const

Constexpr Math Functions

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问题 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 for a function like sqrt I could probably write my own constexpr, but something like sin or cos would be trickier so is there a way around it. 回答1: Actually, because of old and annoying legacy, almost none of the math functions can be constexpr ,

Rounding up and down a number C++

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问题 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 ceil library to get the average of 3 items. results = ceil((marks1 + marks2 + marks3)/3) However, the ceil only rounds the number down but does not roll the number up. There\'s 1 algorithm i stumbled upon var roundedVal = Math.round(origVal*20)

Is std::abs(0u) ill-formed?

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问题 Given the following program: #include <cmath> int main() { std::abs(0u) ; } gcc and clang disagree on whether this is ill-formed. Using gcc with libstdc++ the code builds without error or warning ( see it live ), while using clang with libc++ it generates the following error ( see it live ): error: call to \'abs\' is ambiguous std::abs(0u) ; ^~~~~~~~ Which result is correct? Should abs(0u) be ambiguous or not? MSalters points out an interesting related question: Template version of std::abs.

Sin and Cos give unexpected results for well-known angles

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问题 I am sure this is a really stupid question, but when I pass an angle of 180 degrees into c/c++\'s cos() and sin() functions I appear to receive an incorrect value. I know that it should be: sin of 0.0547 and cos of 0.99 but I get sin of 3.5897934739308216e-009 and cos of -1.00000 My code is: double radians = DegreesToRadians( angle ); double cosValue = cos( radians ); double sinValue = sin( radians ); DegreesToRadians() is: double DegreesToRadians( double degrees ) { return degrees * PI / 180