C ++中两个向量的元素乘法
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element-wise multiplication of two vectors in c++
提问by Dnaiel
I am trying to do the following mathematical operation with two vectors:
我正在尝试使用两个向量进行以下数学运算：
v1 = [a1][a2][a3][a4][a5]
v2 = [b1][b2][b3][b4]b5]
Want to compute:
想要计算：
v = [a2*b2][a3*b3][a4*b4][a5*b5]
Note that I did not want the first element in the new vector.
请注意，我不想要新向量中的第一个元素。
I was wondering if there is a more efficient (one-liner) way to multiply (element-wise) two vectors in c++ than a for-loop (using push back). My current approach is as follows,
我想知道是否有比 for 循环（使用推回）更有效的（单行）方法在 c++ 中（按元素）乘以两个向量。我目前的做法如下，
for(long i=1;i < v1.size();++i){
v.push_back(v1[i]*v2[i]);
}
I also tried the following,
我也尝试了以下，
for (long i = 1; i < v1.size(); ++i){
v[i-1] = v1[i]*v2[i];
}
Any suggestions?
有什么建议？
回答by David Rodríguez - dribeas
std::transform( v1.begin()+1, v1.end(),
v2.begin()+1, v.begin(), // assumes v1,v2 of same size > 1,
// v one element smaller
std::multiplies<int>() ); // assumes values are 'int'
You can replace v.begin()with std::back_inserter(v)if vis empty, you should reserve()memory upfront to avoid multiple allocations.
您可以替换v.begin()为std::back_inserter(v)如果v为空，您应该reserve()预先存储以避免多次分配。
回答by David Stone
You could look into std::valarray. It's designed to allow mathematical operations on every element in the array.
您可以查看std::valarray。它旨在允许对数组中的每个元素进行数学运算。
