具有最大函数的怪异行为

Weird behavior with max function

本文关键字：函数      更新时间：2023-10-16

我有这个代码：

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

方法：angleBetweenVectors返回一个float。

我看不出这个代码在做什么，也看不出它为什么要构建，括号没有正确匹配，我担心这会导致错误。我如何才能获得对angleBetweenVectors的所有调用的最大值？

添加一些索引，即可获得：

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

也就是说，它将返回angleBetweenVectors(robustNormal, normalAtE);的值，因为您缺少max

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

#include <algorithm>
//...
largestDeviation = std::max(
{
   angleBetweenVectors( robustNormal, normalAtA ), 
   angleBetweenVectors( robustNormal, normalAtB ),
   angleBetweenVectors( robustNormal, normalAtC ), 
   angleBetweenVectors( robustNormal, normalAtD ), 
   angleBetweenVectors( robustNormal, normalAtE )
} );

至于您的代码，它将确定函数angleBetweenVectors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。函数std::max的结果以及下一个调用（如果该函数在封闭的std::max调用中使用）。

顺便说一句，你的代码有一个编译错误。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)
);

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，更一致的是，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);

C++11

#include <algorithm>
largestDeviation = std::max({
   angleBetweenVectors(robustNormal, normalAtA),
   angleBetweenVectors(robustNormal, normalAtB),
   angleBetweenVectors(robustNormal, normalAtC),
   angleBetweenVectors(robustNormal, normalAtD),
   angleBetweenVectors(robustNormal, normalAtE)
});

// 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));
}
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