matlab - 特定matlab代码的矢量化

Question

我需要对以下 matlab 代码进行矢量化处理，现在对于较大的矩阵 A 和多重向量 m 来说速度很慢:

function cA = condenseM(A,m)
% condensation of full matrix A (MxM) to type matrix (MxT)
% m is vector of type multiplicities [m1, ...,mT], where 
% M = sum(m) 

% M,T
M = sum(m);
T = length(m);

% "0" + last item index over all types
blockTypeIndx = [0 cumsum(m)];

% condensed matrix generation
cA = zeros(M,T);
for i = 1:T
    if m(i) > 1
       cA(:,i) = max(A(:,blockTypeIndx(i)+1:blockTypeIndx(i+1)),[],2);
    else
       cA(:,i) = A(:,blockTypeIndx(i)+1:blockTypeIndx(i+1));
    end
end
end

这是矩阵 A (6x6) 的简单且足够通用的示例:

 A =

 0     3     3   |  1     1  |   6
 4     0     0   |  0     0  |   2
 0     0     0   |  5     0  |   0
 0     1     1   |  4     4  |   1
 2     0     0   |  0     0  |   5
 0     0     0   |  0     3  |   0
       m1=3          m2 = 2     m3=1

T=3 情况下的多重向量 m:

 m =
 3     2     1

压缩矩阵 cA 如下所示:

 cA = condenseM(A,m)
 cA = 

 3     1     6
 4     0     2
 0     5     0
 1     4     1
 2     0     5
 0     3     0

Answer 1

这是使用 cellfun 进行矢量化的可能代码，但在我的机器上它比你循环的要慢:

cb=cell2mat(cellfun(@(x) max(x,[],2),mat2cell(A,length(A),m),'Uniformoutput',false));