Multiply only certain columns in a matrix with a constant

Question

dj1du 2022-7-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1769765-multiply-only-certain-columns-in-a-matrix-with-a-constant

回答： Star Strider 2022-7-28

Hello,

I have a 100x9 matrix M, whose last six columns should be multiplied by a constant c and the first three columns shall remain unchanged. What would be an appropriate way to achieve this?

Thank you very much for your help!

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Answer 1

Star Strider 2022-7-28

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https://ww2.mathworks.cn/matlabcentral/answers/1769765-multiply-only-certain-columns-in-a-matrix-with-a-constant#answer_1016900

在 MATLAB Online 中打开

Another approach —

M = rand(5,9)                                       % Shorter Version Of 'M'
M = 5×9
    0.7412    0.4804    0.7538    0.9349    0.9716    0.1276    0.5271    0.2733    0.5096
    0.1520    0.6185    0.9599    0.8982    0.1722    0.2804    0.0377    0.0279    0.3176
    0.0054    0.8282    0.3499    0.7655    0.1470    0.0558    0.5818    0.7755    0.2665
    0.7992    0.0395    0.8887    0.5188    0.6443    0.1080    0.8812    0.9678    0.3667
    0.5886    0.9454    0.6386    0.2229    0.4535    0.2106    0.0983    0.3908    0.9509
c = 1000;                                           % Create 'c'
Mnew = M.*[ones(1,3) ones(1,6)*c]                   % Multiply
Mnew = 5×9
    0.7412    0.4804    0.7538  934.8765  971.5514  127.5821  527.1396  273.2641  509.6324
    0.1520    0.6185    0.9599  898.1878  172.1874  280.4265   37.6542   27.8550  317.6187
    0.0054    0.8282    0.3499  765.5312  147.0171   55.8182  581.7670  775.5124  266.5422
    0.7992    0.0395    0.8887  518.8324  644.2832  107.9574  881.2123  967.8147  366.6843
    0.5886    0.9454    0.6386  222.9475  453.5469  210.5717   98.2724  390.7578  950.9357