如何在 MATLAB 匿名函数中集成条件？

Question

我下面的代码非常耗时，因为 A 矩阵很大 (150,000^2)。我可以将条件作为函数 @(x) 集成到 accumarray 中吗？这样我就可以对所有行 b 进行基于单元格的处理，而不必转换为 double 并应用条件？我认为它会快得多！非常感谢！

tic
[a b c]=find(A.'); %extract the positions of non-zero elements of A
add_sym=accumarray(b,c,[],@(x){x}); % re-arrange the values of same row b
add_r = [];
for i = 1:size(add_sym) % go through every row to check the conditions
    r = vertcat(add_sym{i})';  % inverting cell into double vector
    if size(r,2)==1  % and apply the 3 conditions for each row
        add_r0 = 0;
    elseif size(r,2) > 1 && any(r<2)== 0 % many 2s
        add_r0 = r;
        add_r0(1)   = -2;
        add_r0(end) = 2;
        add_r0(2:end-1) = 0;
    elseif size(r,2) > 1 && any(r<2)~= 0 % 2 and 1
        k = find(diff(r)==-1); % find right 2 position
        add_r0 = r;
        add_r0(1)   = -1;
        add_r0(end) = -1;
        add_r0(k) = 2;
        add_r0(2:k-1) = 0;
        add_r0(k+1:end-1) = 0;
    end    
    add_r = [add_r; add_r0']; % saving the replaced values as vectors
end   
ADD = sparse(b,a,add_r,nm,nm,nzmax); % put it back to the same position of sparse matrix A (with replaced value)

toc

此代码是为here

提出的问题编写的

Answer 1

原则上，您正在遍历稀疏 A 矩阵的行。显式提取行并进行检查可能更方便，而不是转换为单元格并返回。我的尝试：

% dummy A, contains 0, 1 or 2's at random
N = 1e4;
A = sparse(randi(2,[N,N])); % A contains 1's and 2's
A(rand([N,N])<0.8) = 0; % randomly delete 80%

tic
add_r = zeros([nnz(A),1]);
iter = 0;
for n=1:size(A,1)
    tmp = A(n,:);
    iter_incr = nnz(tmp);
    if iter_incr==1 % no need to set add_r element to zero
        %
    elseif iter_incr>0
        if ~any(tmp(tmp>0)<2)
            add_r(iter+1) = -2;
            add_r(iter+iter_incr) = 2;
        else
            add_r(iter+1) = -1;
            add_r(iter+iter_incr) = -1;
            add_r(iter+find(tmp(tmp>0)==2)) = 2;
        end
    end

    % increment
    iter = iter + iter_incr;
end
toc

这在我的笔记本电脑上运行大约 20 秒，几分钟后我不得不终止你的解决方案。请注意，我目前无法测试更大的矩阵，这是一个 10000 x 10000 的矩阵，可能与您的数据结构不太相似。

如何在 MATLAB 匿名函数中集成条件？

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