填充增强矢量或矩阵

Question

是否有单表达式方法将标量分配给boost矩阵或向量的所有元素？我正试图找到一种更紧凑的表达方式:

boost::numeric::ublas::c_vector<float, N> v;
for (size_t i=0; i<N; i++) {
    v[i] = myScalar;
 }

以下不起作用:

boost::numeric::ublas::c_vector<float, N> 
   v(myScalar, myScalar, ...and so on..., myScalar);

boost::numeric::ublas::c_vector<float, N> v;
v = myScalar;

Answer 1

因为矢量模型是标准的随机访问容器,所以您应该能够使用标准的STL算法.就像是:

c_vector<float,N> vec;
std::fill_n(vec.begin(),N,0.0f);

要么

std::fill(vec.begin(),vec.end(),0.0f);

它可能也与Boost.Assign兼容,但你必须检查.

Answer 2

我已经开始使用boost::assign我想要静态分配特定值的情况(从上面的链接中提取的示例).

#include <boost/assign/std/vector.hpp>
using namespace boost::assign; // bring 'operator+()' into scope

{
  vector<int> values;
  values += 1,2,3,4,5,6,7,8,9;
}

您也可以boost::assign用于地图.

#include <boost/assign/list_inserter.hpp>
#include <string>
using boost::assign;

std::map<std::string, int> months;
insert( months )
        ( "january",   31 )( "february", 28 )
        ( "march",     31 )( "april",    30 )
        ( "may",       31 )( "june",     30 )
        ( "july",      31 )( "august",   31 )
        ( "september", 30 )( "october",  31 )
        ( "november",  30 )( "december", 31 );

您可以允许使用list_of()和直接分配map_list_of()

#include <boost/assign/list_of.hpp> // for 'list_of()'
#include <list>
#include <stack>
#include <string>
#include <map>
using namespace std;
using namespace boost::assign; // bring 'list_of()' into scope

{
    const list<int> primes = list_of(2)(3)(5)(7)(11);
    const stack<string> names = list_of( "Mr. Foo" )( "Mr. Bar")
                                       ( "Mrs. FooBar" ).to_adapter();

    map<int,int> next = map_list_of(1,2)(2,3)(3,4)(4,5)(5,6);

    // or we can use 'list_of()' by specifying what type
    // the list consists of
    next = list_of< pair<int,int> >(6,7)(7,8)(8,9);

}

也有对功能repeat(),repeat_fun()和range()它允许你添加重复的值或值的范围.

Answer 3

推荐的方式如下所示:

boost::numeric::ublas::c_vector<float, N> v;
v = boost::numeric::ublas::zero_vector<float>(N);
v = boost::numeric::ublas::scalar_vector<float>(N, value);

矩阵类型也是如此:

boost::numeric::ublas::matrix<float> m(4,4);
m = boost::numeric::ublas::identity_matrix<float>(4,4);
m = boost::numeric::ublas::scalar_matrix<float>(4,4);
m = boost::numeric::ublas::zero_matrix<float>(4,4);