MATLAB向量化 [英] MATLAB vectorize

问题描述

我想知道是否有人可以帮助我将这段代码向量化.

I was wondering if anyone could help me vectorize this piece of code.

fr_bw是一个矩阵.

fr_bw is a matrix.

 for i=1:height
   for j=1:width      
                [min_w, min_w_index] = min(w(i,j,:));  
                mean(i,j,min_w_index) = double(fr_bw(i,j));
                sd(i,j,min_w_index) = sd_init;
     end
end

推荐答案

对于这些sif (match == 0)内容，我无能为力-如果应该是if (match == 0)，则您无需更改match，因此可以被带到循环之外.

I can't help you with this sif (match == 0) stuff -- if it's supposed to be if (match == 0) you're not changing match so it could be brought outside the loop.

否则，如何处理?

[min_w, min_w_index] = min(w, [], 3);
r = repmat((1:height)',1,width);
c = repmat(1:width,height,1);
ind = sub2ind(size(w),r(:),c(:),min_w_index(:));
w_mean(ind) = double(fr_bw);
w_sd(ind) = repmat(sd_init,height,width);

(请注意，mean是内置函数，因此我将您的变量重命名为w_mean和w_sd.)

(Please note that mean is a built-in function so I renamed your variables to w_mean and w_sd.)

sub2ind调用为您提供与下标相对应的线性索引. (直接下标将不起作用； z([a1 a2 a3],[b1 b2 b3],[c1 c2 c3])引用z数组中的27个元素，而下标是指定下标的笛卡尔积，而不是您可能期望的z(a1,b1,c1)和z(a2,b2,c2)和z(a3,b3,c3) )

The sub2ind call gives you linear indices that correspond to subscripts. (Direct subscripts won't work; z([a1 a2 a3],[b1 b2 b3],[c1 c2 c3]) refers to 27 elements in the z array with subscripts that are the cartesian product of the specified subscripts, rather than z(a1,b1,c1) and z(a2,b2,c2) and z(a3,b3,c3) that you might expect.)

以下是此技术的说明:

>> height = 6; width = 4;
>> w = randi(1000,height,width,2)

w(:,:,1) =

   426   599    69   719
   313   471   320   969
   162   696   531   532
   179   700   655   326
   423   639   408   106
    95    34   820   611


w(:,:,2) =

   779   441   638   696
   424   528   958    68
    91   458   241   255
   267   876   677   225
   154   519   290   668
   282   944   672   845

>> [min_w, min_w_index] = min(w, [], 3);
>> min_w_index

min_w_index =

     1     2     1     2
     1     1     1     2
     2     2     2     2
     1     1     1     2
     2     2     2     1
     1     1     2     1

>> z = zeros(height,width,2);
>> r = repmat((1:height)',1,width);
>> c = repmat(1:width,height,1);
>> ind = sub2ind(size(w),r(:),c(:),min_w_index(:));
>> z(ind) = 1

z(:,:,1) =

     1     0     1     0
     1     1     1     0
     0     0     0     0
     1     1     1     0
     0     0     0     1
     1     1     0     1


z(:,:,2) =

     0     1     0     1
     0     0     0     1
     1     1     1     1
     0     0     0     1
     1     1     1     0
     0     0     1     0

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