How can I know what element a value came from in a vector?

Question

Roland 2011-2-22

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https://ww2.mathworks.cn/matlabcentral/answers/1811-how-can-i-know-what-element-a-value-came-from-in-a-vector

I just started using Matlab. I found my minimum value of a given vector, but I need to know what the corresponding value is in another vector. Is there a way to know where the exact element is?

I need to know my "r" value for the cheapest.

    v=600;
    r=[1:.1:100];
    h=(v-2.*pi.*((r.^3)./3))./(pi.*r.^2);
    cost=(400.*(2.*pi.*r.*h))+(600.*(2.*pi.*r.^2));
    cheapest=min(cost)  
   cheapest =
   1.4825e+005

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Answer 1

Walter Roberson 2011-2-22

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https://ww2.mathworks.cn/matlabcentral/answers/1811-how-can-i-know-what-element-a-value-came-from-in-a-vector#answer_2694

在 MATLAB Online 中打开

[cheapest, cheapidx] = min(cost);

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Answer 2

Oleg Komarov 2011-2-22

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https://ww2.mathworks.cn/matlabcentral/answers/1811-how-can-i-know-what-element-a-value-came-from-in-a-vector#answer_2695

在 MATLAB Online 中打开

Use the second output of min:

[cheapest, pos] = min(cost); 
r(pos)

Oleg

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Answer 3

Paulo Silva 2011-2-22

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1811-how-can-i-know-what-element-a-value-came-from-in-a-vector#answer_2696

在 MATLAB Online 中打开

    v=600;
    r=[1:.1:100];
    h=(v-2.*pi.*((r.^3)./3))./(pi.*r.^2);
    cost=(400.*(2.*pi.*r.*h))+(600.*(2.*pi.*r.^2));
    cheapest=min(cost); 
    Minr=r(cost==cheapest) %The r value that minimizes the cost function
    %check if the value is correct on a figure
    clf
    hold on
    plot(r,cost) %draw the cost function
    plot(Minr,cheapest,'rx') %mark the minimum value
    axis([0 10 0 5e5])
    grid on