cmath

问题 I am trying to use tgamma() from the standard library. When I try to compile, I get the error message: Call to undefined function tgamma I have the directive #include <cmath> . I use Embarcadero C++ Builder XE3, which claims to support C++11 standards. What could be my problem, and how to fix it? 回答1: Boost contains a tgamma function. #include <boost/math/special_functions/gamma.hpp> ... double rootPi = boost::math::tgamma<double>(0.5); Of course, you can always switch to a different compiler

问题 Are cmath exp() and log() functions always symmetrical? Ergo if I do double x; double y = exp(log(x)); assert(x == y); will the assert ever fail, and in that case: under what circumstances? We can assume that x is a rational number > 0 . 回答1: A floating-point log cannot be one-to-one. It needs to be monotone increasing and satisfy log(64) > 4.15 and log(128) < 4.86 . There are 2 52 double s between 64 and 128, but there are fewer than 2 50 double s between 4.15 and 4.86. There are multiple

问题 Randomly building a very easy sound spectrum analyzer. Given this python code: http://rosettacode.org/wiki/Fast_Fourier_transform#Python Implemented like this: import math from cmath import exp, pi def fft(x): N = len(x) if N <= 1: return x even = fft(x[0::2]) odd = fft(x[1::2]) return ([even[k] + exp(-2j * pi * k / N) * odd[k] for k in xrange(N / 2)] + [even[k] - exp(-2j * pi * k / N) * odd[k] for k in xrange(N / 2)]) #res = fft([1.0, 1.0, 1.0, 1.0, 0.0, 0.0, 0.0, 0.0]) res = [math.sin(k) /

问题 [I globally edited the question to be more "useful" and clear] I was wondering about the complexity of the implementation of the function exp in cmath. By complexity, I mean algorithmic complexity if possible. Otherwise cost compared to a floating point operation (addition for example) The following lines : double x = 3; double y = std::exp(x); compile to : ... 19,23d16 movq %rax, -40(%rbp) movsd -40(%rbp), %xmm0 call exp movsd %xmm0, -40(%rbp) movq -40(%rbp), %rax ... exp has to be

问题 I've written a small program that utilizes the Fast Light Toolkit and for some reason a compiler error is generated when trying to access the functions in the cmath header. Such as error ::acos has not been declared. This goes on for pretty much every function it tries to use in the header. What could I be missing? The header files I have included are Simple_window.h Graph.h both of which are part of the FLTK. The code is this: #include "Simple_window.h" // get access to our windows library

问题 I got this python code for FFT calculation of a sound signal: from math import * from cmath import exp, pi def fft(x): N = len(x) if N <= 1: return x even = fft(x[0::2]) odd = fft(x[1::2]) return ([even[k] + exp(-2j * pi * k / N) * odd[k] for k in xrange(N / 2)] + [even[k] - exp(-2j * pi * k / N) * odd[k] for k in xrange(N / 2)]) N = 64 res = [sin(k) for k in xrange(N)] # Window function a = 2*pi/(N-1) for k in xrange(N): z = a * res[k] res[k] = 0.42659 - 0.49656*cos(z) + 0.076849*cos(2*z)

问题 Through unfortunate circumstances I have discovered that my standard library implementations <math.h> and <cmath> (C++) apparently contain a definition for a function with a prototype like: double gamma(double x); Though I do not see it listed anywhere in the language standard (draft I have access to). Using gcc v4.2.1 on Mac OS X that function evaluates the same as tgamma which is actually the name given to it in the standard. (reference) But on gcc v4.6.3 on Ubuntu 12.04 that function

问题 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 2013 (v120) : float f1= abs(-9.2); // f = 9.2 float f2= fabs(-9); // Compile error [*] So fabs(-9) it will give me a compiler error, but when I tried to do the following: double i = -9; float f2= fabs(i); // This will work fine What I understand

问题 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 <typename T> inline T abs(const T& v) { return v < 0 ? -v : v; } 回答1: See LWG issue 2192. Currently, std::abs(x-y) < 2 fails if x and y are unsigned. This catches a subtle programming error. With the proposed change, it compiles but does entirely the wrong this. abs(3u-4u) would be much larger than 2, in fact it's UINT_MAX . 回答2:

问题 This question already has answers here : cmath header confusion (4 answers) Closed 6 years ago . I had a problem previously because of functions being overloaded without std:: . And the curse is still happening every now and then because I don't use using namespace std; . Removing using namespace std causes the program to get crap results Is there a way to disable all those non-std functions that come from c and only work with c++ functions under the namespace std (without having to use using