how can I create cumulative matrix.
显示 更早的评论
Hello a question please.
I have matrix P with size (452*500). I want to select random selection with roulette wheel selection. I write something:
r=rand;
c=reshape(p,1,[]);
c1=cumsum(c);
j=find(r<=c1,1,'first');
[j1 j2]=ind2sub(size(p),j);
end
but I want to remove part " c=reshape(p,1,[]);" and create cumulative matrix of p directly without reshaping it to matrix c. How can I do it?
Thank you.
采纳的回答
Something like this? :
r = rand;
jj = find(r<=cumsum(p(:)),1,'first');
[j1,j2] = ind2sub(size(p),jj);
3 个评论
fatema saba
2015-2-3
This depend on you and what you want your code to do. Read the documentation for cumsum, you will see that it always calculates the sum along one dimension (row, column, etc). Lets have a look at what the documentation says:
- If A is a vector, then cumsum(A) returns a vector containing the cumulative sum of the elements of A.
- If A is a matrix, then cumsum(A) returns a matrix containing the cumulative sums for each column of A.
...
- B = cumsum(A,dim) returns the cumulative sum of the elements along dimension dim. For example, if A is a matrix, then cumsum(A,2) returns the cumulative sum of each row.
So the documentation tells us that if you want a column vector of cumulative sums of each row (or a row of the columns, etc), then the answer to your question is yes, you can do it without reshaping the matrix p first. In every case it is summing only along one dimension, so if you want the cumulative sum over all elements of a matrix, you will have to convert it first to a vector, and probably the neatest way of doing this is using p(:).
fatema saba
2015-2-3
更多回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Creating and Concatenating Matrices 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
