最大功能的怪异行为

Question

我有以下代码：

largestDeviation = max(max(max(angleBetweenVectors(robustNormal, normalAtA),
                               angleBetweenVectors(robustNormal, normalAtB)),
                           angleBetweenVectors(robustNormal, normalAtC)),
                       angleBetweenVectors(robustNormal, normalAtD)),
                       angleBetweenVectors(robustNormal, normalAtE);

方法： angleBetweenVectors返回float 。

我看不到这段代码在做什么，以及为什么它实际上在构建，方括号无法正确匹配，恐怕它会导致错误。 如何获得我对angleBetweenVectors的所有调用的angleBetweenVectors ？

Answer 1

添加一些说明，您将获得：

largestDeviation = 
max(
   max(
      max(
         angleBetweenVectors(robustNormal, normalAtA),
         angleBetweenVectors(robustNormal, normalAtB)
      ),
      angleBetweenVectors(robustNormal, normalAtC)
   ),
   angleBetweenVectors(robustNormal, normalAtD)
), 
angleBetweenVectors(robustNormal, normalAtE);

即它将返回angleBetweenVectors(robustNormal, normalAtE);的值angleBetweenVectors(robustNormal, normalAtE); 因为你错过了max

Answer 2

您可以使用标准算法std :: max作为参数std::initializer_list作为参数

#include <algorithm>
//...

largestDeviation = std::max(
{
   angleBetweenVectors( robustNormal, normalAtA ), 
   angleBetweenVectors( robustNormal, normalAtB ),
   angleBetweenVectors( robustNormal, normalAtC ), 
   angleBetweenVectors( robustNormal, normalAtD ), 
   angleBetweenVectors( robustNormal, normalAtE )
} );

对于您的代码，它将确定由angleBetweenVectors函数的相应调用返回的值中的最大值。 该代码使用标准算法std::max ，该算法具有两个参数，并确定两个参数之间的最大值。

例如内部调用

max( angleBetweenVectors(robustNormal, normalAtA ),
     angleBetweenVectors(robustNormal, normalAtB ) ),

查找函数调用返回的两个值之间的最大值。 如果在封闭的std::max调用中依次使用了该函数，则函数std::max以及下一个调用的结果。

顺便说一下，您的代码有编译错误。应该再调用一次std::max

largestDeviation = 

max(
   max(
      max(
         max( angleBetweenVectors(robustNormal, normalAtA ),
              angleBetweenVectors(robustNormal, normalAtB) 
         ),
         angleBetweenVectors(robustNormal, normalAtC)
      ),
      angleBetweenVectors(robustNormal, normalAtD) 
   ),
   angleBetweenVectors(robustNormal, normalAtE)
);

Answer 3

您也可以这样编写代码：

maxAngle = angleBetweenVectors(robustNormal, normalAtA);
maxAngle = max(angleBetweenVectors(robustNormal, normalAtB), maxAngle);
maxAngle = max(angleBetweenVectors(robustNormal, normalAtC), maxAngle);
maxAngle = max(angleBetweenVectors(robustNormal, normalAtD), maxAngle);
maxAngle = max(angleBetweenVectors(robustNormal, normalAtE), maxAngle);

或者，当为maxAngle选择一个好的初始值时，例如，我会说-2*M_PI ：

maxAngle = -2 * M_PI;
maxAngle = max(angleBetweenVectors(robustNormal, normalAtA), maxAngle);
maxAngle = max(angleBetweenVectors(robustNormal, normalAtB), maxAngle);
maxAngle = max(angleBetweenVectors(robustNormal, normalAtC), maxAngle);
maxAngle = max(angleBetweenVectors(robustNormal, normalAtD), maxAngle);
maxAngle = max(angleBetweenVectors(robustNormal, normalAtE), maxAngle);

Answer 4

C ++ 11

#include <algorithm>

largestDeviation = std::max({
   angleBetweenVectors(robustNormal, normalAtA),
   angleBetweenVectors(robustNormal, normalAtB),
   angleBetweenVectors(robustNormal, normalAtC),
   angleBetweenVectors(robustNormal, normalAtD),
   angleBetweenVectors(robustNormal, normalAtE)
});

Answer 5

// Store all your normals in a vector
std::vector<normal> normals;
normals.push_back(normalAtA);
normals.push_back(normalAtB);
normals.push_back(normalAtC);
normals.push_back(normalAtD);
normals.push_back(normalAtE);

// Iterate through your vector, and check each angle to see if it is the new max
max_val = 0;
vector<normal>::iterator it;
for (it = normals.begin(); it != normals.end(); ++it)
{
    max_val = max(max_val, angleBetweenVectors(robustNormal, *it));
}