生成在MATLAB

Question

特定矩阵I具有矩阵： x=[0 0 0;5 8 0; 7 6 0]

欲矩阵： m=[0 0 0;5 8 0;7 6 0; 0 0 8;5 8 8;7 6 8; 0 0 16;5 8 16;7 6 16]

我想，而其他两列保持相同的是矩阵x的第三列得到由8各自时间乘以。我希望这样继续下去，直到第三列的值达到72为止。

我该怎么用bsxfun或其他方式来做到这一点？

Answer 1

假设下面的两个假设，你可以尝试其后列出的方法 -

1. 继续adding而不是multiplying。
2. 全部最后元素column-3至少达到72。

方法＃1随着bsxfun]

stopn = 72; %// stop adding till this number 
add_factor = 8; %// Add factor to be added at each iteration to get to 72 
ntimes = ceil(max((stopn - x(:,3))/add_factor)) %// no. of iterations needed 

%// Get the starting 2d version of matrix to be added to x iteratively 
x_add_2d = zeros(size(x)); %// 
x_add_2d(:,3) = add_factor; 

%// Get the complete version of matrix to be added (in 3d), then add to x 
x_add_3d = bsxfun(@plus,x,bsxfun(@times,x_add_2d,permute([0:ntimes],[1 3 2]))) 

%// Concatenate along rows to form a 2D array as the final output 
out = reshape(permute(x_add_3d,[1 3 2]),size(x_add_3d,1)*(ntimes+1),[]) 

方法2 [附repmat]

stopn = 72; %// stop adding till this number 
add_factor = 8; %// Add factor to be added at each iteration to get to 72 
ntimes = ceil(max((stopn - x(:,3))/add_factor)); %// no. of iterations needed 

out = repmat(x,[ntimes+1 1]) %// replicated version of x 
add_col3 = repmat([0:8:ntimes*8],size(x,1),1) %// column-3 values to be added 
out(:,3) = out(:,3) + add_col3(:) %// add those for the final output 

---

样品运行 -

x = 
    52 43 57 
    41 40 48 
    41 49 50 
out = 
    52 43 57 
    41 40 48 
    41 49 50 
    52 43 65 
    41 40 56 
    41 49 58 
    52 43 73 
    41 40 64 
    41 49 66 
    52 43 81 
    41 40 72 
    41 49 74 

Answer 2

据我了解，你可以使用repmat和kron做到这一点：

clear 
clc 

x=[0 0 0;5 8 0; 7 6 0]; 

%// Generate last column containing the values form 0 to 72, each repeated 3 times. 
y = kron(0:8:72,ones(1,3)) 

%// The first 2 columns remain the same, so we just repeat them 10 times. 

out = [repmat(x(:,1:2),10,1) y(:)] 

用方括号来连接，输出是这样的：

out = 

0  0  0 
5  8  0 
7  6  0 
0  0  8 
5  8  8 
7  6  8 
0  0 16 
5  8 16 
7  6 16 
0  0 24 
5  8 24 
7  6 24 
0  0 32 
5  8 32 
7  6 32 
0  0 40 
5  8 40 
7  6 40 
0  0 48 
5  8 48 
7  6 48 
0  0 56 
5  8 56 
7  6 56 
0  0 64 
5  8 64 
7  6 64 
0  0 72 
5  8 72 
7  6 72