function handle error with matirx

Question

harley 2013-8-28

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/85768-function-handle-error-with-matirx

i get the error below, any ideas where i've gone wrong? Also with the way i've wrote my D & L vectors will D(1) and the corresponding L(1) be used together in further calculations.

%F  ZERO cannot continue because user supplied function_handle ==>      %@(x)1/sqrt(x)+2*log10(eoverD/3.7+2.51/Re/sqrt(x))
%failed with the error below.
%Matrix dimensions must agree.
%Error in ==> Q1_check_2 at 22
%f = fzero(darbyFormula,4);
    D = [0.1, 0.2, 0.05, 0.15]; 
    L = [10, 3, 4, 8]; 
    A = 0.25*pi.*D.^2; 
    e = 0.0015e-3; 
    rho = 998; 
    nu = 1.01e-6;  
    eoverD = e./D;
    alpha = 0.1;
    %
    Vo = 2;
    for Vn = 2:0.1:30;. 
    Re = (D.*Vo) / nu;
    if Re < 2300
    f = 64 / Re;
    else
       darbyFormula = @(x) 1/sqrt(x)+2*log10(eoverD/3.7 + 2.51/Re/sqrt(x));
    f = fzero(darbyFormula,0.01);
    end
    %
    dPloss = (f*rho*(L./D)) * ((Vn.*Vo)./2);
    Va = (alpha*Vn)+((1-alpha)*Vo); 
    Vo = Va;
    end

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Answer 1

the cyclist 2013-8-28

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/85768-function-handle-error-with-matirx#answer_95274

You cannot call fzero() with Re as a vector, in the way that you have done. You need to solve for each value of Re individually. (Also, your if statement will not work as you intend, as written.)

Rather than trying to do all values of (D,L) at once, I suggest you just write a loop over those values.