For loop vector issue

Question

Christian Boaitey 2022-3-26

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1681409-for-loop-vector-issue

回答： Christian Boaitey 2022-3-26

Hi all,

I am in the midst of programming some code for a university assignment, however, I'm having some trouble with my for loop.

I want to save the values from the for loop for the variable 'Sb'. However, when using 'Sb(e)', I get "Array indices must be positive integers or logical values". When running the code without 'Sb(e)' it runs fine but I just don't get the intermediate values in between. Much help appreciated!

clc
clear
%% Constants
Dp=125e-3;
Dm=45e-3;
Lp=1500e-3;
Lk=215e-3;
alpha=5;
g=9.81;
k=1.2336;
R=350.7;
T0=2322;
%% Part A
w=(Dp-Dm)/2;
Gc=((w*cosd(alpha)-Lk*sind(alpha))/(1-sind(alpha)));
gamma=sqrt(k)*(2/(k+1))^((k+1)/(2*k-1));
C=sqrt((R*T0)/gamma);
for e=0:0.01:w
    if e<=Gc
        Rv=(Dm/2)+Lk*tand(alpha)+e.*((1-e.*sind(alpha)/cosd(alpha)));
    elseif e>=Gc
        Rv=Dp/2;   
    end
Rm=(Dm/2)+e;
Sb=2*pi*Rm*(Lp-Lk-e*tand(alpha/2))+(Rv^2-Rm^2)*(pi/sind(alpha));
Sbvec(e)=Sb
end

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Answer 1

Torsten 2022-3-26

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1681409-for-loop-vector-issue#answer_927729

编辑：Torsten 2022-3-26

在 MATLAB Online 中打开

E = 0:0.01:w;
n = numel(E);
for i = 1:n
  e = E(i);
    ...
  Sbvec(i) = Sb;
end

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Answer 2

Walter Roberson 2022-3-26

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1681409-for-loop-vector-issue#answer_927724

在 MATLAB Online 中打开

e_values = 0:0.01:w;
num_e = length(e_values);
Sbvec = zeros(num_e, 1);
for e_idx = 1 : num_e
    e = e_values(e_idx);
    if e<=Gc
        Rv=(Dm/2)+Lk*tand(alpha)+e.*((1-e.*sind(alpha)/cosd(alpha)));
    elseif e>=Gc
        Rv=Dp/2;
    else
        error('comparison case not accounted for')
    end
    Rm=(Dm/2)+e;
    Sb=2*pi*Rm*(Lp-Lk-e*tand(alpha/2))+(Rv^2-Rm^2)*(pi/sind(alpha));
    Sbvec(e_idx)=Sb;
end