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| Complex numbers | |||||||||||||||||||||||||||||||
Numeric array (valarray) | |||||||||||||||||||||||||||||||
| Pseudo-random number generation | |||||||||||||||||||||||||||||||
| Bit manipulation(C++20) | |||||||||||||||||||||||||||||||
| Saturation arithmetic(C++26) | |||||||||||||||||||||||||||||||
| Factor operations | |||||||||||||||||||||||||||||||
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| Interpolations | |||||||||||||||||||||||||||||||
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| Generic numeric operations | |||||||||||||||||||||||||||||||
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| C-style checked integer arithmetic | |||||||||||||||||||||||||||||||
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Defined in header <cmath> | ||
| (1) | ||
float expint(float num); double expint(double num); | (since C++17) (until C++23) | |
/* floating-point-type */ expint(/* floating-point-type */ num); | (since C++23) | |
float expintf(float num); | (2) | (since C++17) |
longdouble expintl(longdouble num); | (3) | (since C++17) |
Defined in header <cmath> | ||
template<class Integer> double expint( Integer num); | (A) | (since C++17) |
std::expint for all cv-unqualified floating-point types as the type of the parameternum.(since C++23)Contents |
| num | - | floating-point or integer value |
| e-t |
| t |
Errors may be reported as specified inmath_errhandling.
Implementations that do not support C++17, but supportISO 29124:2010, provide this function if__STDCPP_MATH_SPEC_FUNCS__ is defined by the implementation to a value at least 201003L and if the user defines__STDCPP_WANT_MATH_SPEC_FUNCS__ before including any standard library headers.
Implementations that do not support ISO 29124:2010 but support TR 19768:2007 (TR1), provide this function in the headertr1/cmath and namespacestd::tr1.
An implementation of this function is alsoavailable in boost.math.
The additional overloads are not required to be provided exactly as(A). They only need to be sufficient to ensure that for their argumentnum of integer type,std::expint(num) has the same effect asstd::expint(static_cast<double>(num)).
#include <algorithm>#include <cmath>#include <iostream>#include <vector> template<int Height=5,int BarWidth=1,int Padding=1,int Offset=0,class Seq>void draw_vbars(Seq&& s,constbool DrawMinMax=true){ static_assert(0< Height and0< BarWidth and0<= Padding and0<= Offset); auto cout_n=[](auto&& v,int n=1){while(n-->0)std::cout<< v;}; constauto[min, max]=std::minmax_element(std::cbegin(s),std::cend(s)); std::vector<std::div_t> qr;for(typedef decltype(*std::cbegin(s)) V; V e: s) qr.push_back(std::div(std::lerp(V(0),8* Height,(e-*min)/(*max-*min)),8)); for(auto h{Height}; h-->0; cout_n('\n')){ cout_n(' ', Offset); for(auto dv: qr){constauto q{dv.quot}, r{dv.rem};unsignedchar d[]{0xe2,0x96,0x88,0};// Full Block: '█' q< h? d[0]=' ', d[1]=0: q== h? d[2]-=(7- r):0; cout_n(d, BarWidth), cout_n(' ', Padding);} if(DrawMinMax&& Height>1) Height-1== h?std::cout<<"┬ "<<*max: h?std::cout<<"│ ":std::cout<<"┴ "<<*min;}} int main(){std::cout<<"Ei(0) = "<< std::expint(0)<<'\n'<<"Ei(1) = "<< std::expint(1)<<'\n'<<"Gompertz constant = "<<-std::exp(1)* std::expint(-1)<<'\n'; std::vector<float> v;for(float x{1.f}; x<8.8f; x+=0.3565f) v.push_back(std::expint(x)); draw_vbars<9,1,1>(v);}
Output:
Ei(0) = -infEi(1) = 1.89512Gompertz constant = 0.596347 █ ┬ 666.505 █ │ ▆ █ │ █ █ │ █ █ █ │ ▆ █ █ █ │ ▁ ▆ █ █ █ █ │ ▂ ▅ █ █ █ █ █ █ │▁ ▁ ▁ ▁ ▁ ▁ ▁ ▂ ▂ ▃ ▃ ▄ ▆ ▇ █ █ █ █ █ █ █ █ ┴ 1.89512
| Weisstein, Eric W. "Exponential Integral." From MathWorld — A Wolfram Web Resource. |
