How can I multiply a vector by a scaling value with a loop?

Question

Paola 2022-2-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1653190-how-can-i-multiply-a-vector-by-a-scaling-value-with-a-loop

评论： Jan 2022-2-18

Hi I have a vector A (1x200) and I want to multiply it for a scaling factor of 0.2 for 10 times. I would like to obtain a matrix B(10x200) where each row is the scaled vector?

thanks

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Answer 1

Jan 2022-2-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1653190-how-can-i-multiply-a-vector-by-a-scaling-value-with-a-loop#answer_899580

编辑：Jan 2022-2-18

在 MATLAB Online 中打开

A = rand(1, 100);
S = 0.2 .^ (1:10).';
B = S .* A;

A smaler example:

A = rand(1, 4)
A = 1×4
    0.3654    0.1529    0.0723    0.4163
S = 0.2 .^ (1:3).'
S = 3×1
    0.2000
    0.0400
    0.0080
B = S .* A
B = 3×4
    0.0731    0.0306    0.0145    0.0833
    0.0146    0.0061    0.0029    0.0167
    0.0029    0.0012    0.0006    0.0033

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Voss 2022-2-18

编辑：Voss 2022-2-18

在 MATLAB Online 中打开

I believe that is what @Jan's answer does (using 5 elements here instead of 100 for ease of display):

A = rand(1, 5);
S = 0.2 .^ (1:10).';
B = S .* A;
format long
disp(A);
   0.928773205480852   0.372047849369982   0.597515763533504   0.191352119560953   0.541467764860118
disp(B);
   0.185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
   0.037150928219234   0.014881913974799   0.023900630541340   0.007654084782438   0.021658710594405
   0.007430185643847   0.002976382794960   0.004780126108268   0.001530816956488   0.004331742118881
   0.001486037128769   0.000595276558992   0.000956025221654   0.000306163391298   0.000866348423776
   0.000297207425754   0.000119055311798   0.000191205044331   0.000061232678260   0.000173269684755
   0.000059441485151   0.000023811062360   0.000038241008866   0.000012246535652   0.000034653936951
   0.000011888297030   0.000004762212472   0.000007648201773   0.000002449307130   0.000006930787390
   0.000002377659406   0.000000952442494   0.000001529640355   0.000000489861426   0.000001386157478
   0.000000475531881   0.000000190488499   0.000000305928071   0.000000097972285   0.000000277231496
   0.000000095106376   0.000000038097700   0.000000061185614   0.000000019594457   0.000000055446299

The first row of B is 0.2*A, and each successive row is 0.2 times the previous row.

If you want 10 copies of 0.2*A instead, you can say:

B = repmat(0.2*A,10,1);
disp(B);
185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024
185754641096170   0.074409569873996   0.119503152706701   0.038270423912191   0.108293552972024

Jan 2022-2-18

@Paola : I've inserted a small example. If this does not do, what you need, explain the difference. Give e.g. a small example of what you need instead.

What exactly does this mean: "multiply it for a scaling factor of 0.2 for 10 times"?

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