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#include <boost/math/special_functions/cos_pi.hpp>
namespace boost{ namespace math{ template <class T> calculated-result-type cos_pi(T x); template <class T, class Policy> calculated-result-type cos_pi(T x, const Policy&); }} // namespaces
Returns the cosine of π x.
        The return type of this function is computed using the result
        type calculation rules: the return is double
        when x is an integer type and T otherwise.
      
The final Policy argument is optional and can be used to control the behaviour of the function: how it handles errors, what level of precision to use etc. Refer to the policy documentation for more details.
This function performs exact all-integer arithmetic argument reduction before computing the cosine of π·x.
Table 8.80. Error rates for cos_pi
| 
                  GNU C++ version 7.1.0 | 
                  GNU C++ version 7.1.0 | 
                  Sun compiler version 0x5150 | 
                  Microsoft Visual C++ version 14.1 | |
|---|---|---|---|---|
| sin_pi and cos_pi | Max = 0ε (Mean = 0ε) | Max = 0.991ε (Mean = 0.302ε) | Max = 0.991ε (Mean = 0.302ε) | Max = 0.996ε (Mean = 0.284ε) | 
| sin_pi and cos_pi near integers and half integers | Max = 0ε (Mean = 0ε) | Max = 0.976ε (Mean = 0.28ε) | Max = 0.976ε (Mean = 0.28ε) | Max = 0.996ε (Mean = 0.298ε) |