英文:
Armadillo/C++: How to assign elements from a vector to a cube tube?
问题
假设我有一个3x3x4的立方体Q（即一个具有3行、三列和4切片的立方体），以及一个具有4个元素的列向量C（即与Q的切片数相同的元素）。有没有办法让我使用C来填充Q的一个管道？
我尝试了以下方法：
# include <armadillo>
cube Q(3,3,4);
mat C(4,1, fill::zeros);
Q.tube(0, 0) = C;
但它没有起作用（出现了运行时异常）。有没有办法在不显式循环管道和向量元素的情况下实现这个目标？
已解决
上面的代码完全有效。事实证明，第一次尝试时我可能做了其他事情（不知道是什么）出错了。感谢darcamo指出代码实际上是有效的！
英文:
Suppose I have a 3x3x4 cube Q (i.e. a cube having 3 rows, three columns, and 4 slices) and a column vector C with 4 elements (i.e. as many elements as the slices of Q). Is there a way for me to use C to populate a tube of Q?
I tried the following:
# include <armadillo>
cube Q(3,3,4);
mat C(4,1, fill::zeros);
Q.tube(0, 0) = C;
but it didn't work (got a runtime exception). Is there a way to achieve the goal without looping explicitly through the tube and the vector elements?
SOLVED
The code above works just fine. It turns out I was probably doing something else (don't know what) wrong the first time I tried it. Thanks to darcamo for pointing out the code actually works!
答案1
得分: 1
这很奇怪。我尝试过，对我来说完全正常。在进行赋值之前，尝试将C矩阵转换为arma::vec。
Q.tube(0, 0) = arma::conv_to<arma::vec>::from(C);
由于"tube"是一维的，将完整的二维矩阵分配给它是没有意义的。尽管在你的情况下，它是一个列矩阵，应该可以工作。
我不需要进行转换，但值得尝试，因为由于不同的标志、编译器支持等原因，一些Armadillo中的功能可能不可用。
英文:
That is strange. I try it and it worked just fine for me. Try converting the C matrix into an arma::vec before with the assignment.
Q.tube(0, 0) = arma::conv_to<arma::vec>::from(C);
Since a "tube" is one-dimensional it does not make sense to assign a full 2D matrix to it anyway. Although in your case it's a column matrix and it should work.
I didn't need to convert it, but it is worth trying, since some features in armadillo might not be available due to different flags, compiler support, etc.
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