在matlab中生成一个特定的矩阵

Question

我有矩阵： x=[0 0 0;5 8 0; 7 6 0]

我想要矩阵： 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]

我希望矩阵 x 的第三列每次都乘以 8 而其他两列保持不变。我希望这一直持续到第三列中的值达到 72。

如何使用 bsxfun 或任何其他方式来完成？

Answer 1

据我了解，您可以使用 repmat 和 kron 来完成：

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(:)]

使用方括号拼接，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

Answer 2

假设有以下两个假设，您可以尝试后面列出的方法-

继续 adding 而不是 multiplying。
column-3 中的所有 final 元素至少达到 72。

方法 #1 [使用 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 [使用 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

样本运行-

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

在matlab中生成一个特定的矩阵

generate a specific matrix in matlab

matlab

matrix

bsxfun