what is wrong with my 'For' loop

Question

ameen 2013-6-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/77993-what-is-wrong-with-my-for-loop

this is my FOR loop code

clear all
clc
close all
v=0.5;
d=0.1;
density=1000;
w=0.446;
t=0.2;
rr=30.494*v^5-86.479*v^4+89.045*v^3-34.023*v^2+6.6418*v;
va=v*(1-w);
n=100;
s=rr/(1-t);
for n=100:12000;
  j=va/(n*d);
  kt=0.392*(1-(j/0.95))^0.8;
  TT(n)=kt*density*(n./60)^2*d^4;
  if TT(n)/s>0.9988
      n
      TT(end)
      s
      return
  end
end

and it works just fine, but when i make the input which is v to be a vector from 0.5:0.1:1.5 it is not working and give me that message error

In an assignment A(I) = B, the number of elements in B and I must be the same.

Error in stupidfile (line 17)
  TT(n)=kt*density*(n./60).^2*d^4;

and this is the code,

clear all
clc
close all
v=0.5:0.1:1.5;
d=0.1;
density=1000;
w=0.446;
t=0.2;
rr=30.494*v.^5-86.479*v.^4+89.045*v.^3-34.023*v.^2+6.6418*v;
va=v*(1-w);
n=100;
s=rr/(1-t);
for n=100:12000;
  j=va/(n*d);
  kt=0.392*(1-(j/0.95)).^0.8;
  TT(n)=kt*density*(n./60).^2*d^4;
  if TT(n)/s>0.9988
      n
      TT(end)
      s
      return
  end
end

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Azzi Abdelmalek 2013-6-4

Avoid using clear all

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Answer 1

Azzi Abdelmalek 2013-6-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/77993-what-is-wrong-with-my-for-loop#answer_87684

在 MATLAB Online 中打开

clc
close all
v=[0.2 0.5];
d=0.1;
density=1000;
w=0.446;
t=0.2;
rr=30.494*v.^5-86.479*v.^4+89.045*v.^3-34.023*v.^2+6.6418*v;
va=v*(1-w);
n=100;
s=rr/(1-t);
TT=[];
for n=100:12000;
  j=va/(n*d);
  kt=0.392*(1-(j/0.95)).^0.8;
  TT(end+1,:)=kt*density*(n./60).^2*d.^4;
  if TT(end,:)/s>0.9988
      n
      TT(end,:)
      s
      return
  end
end

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ameen 2013-6-4

Thank you but when i run this code it gives me one results only while i want for every (v) the corresponding (n) so i want to calculate n for v from 0.2 to 1.5

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Answer 2

Mark 2013-6-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/77993-what-is-wrong-with-my-for-loop#answer_87685

In your loop, the calculation: kt*density*(n./60).^2*d^4 gives you a vector (1x11 in your case). You are trying to assign this vector to the nth index of TT. MATLAB can't do that. You either have to loop through the elements, or use some command to select one of the elements to put into TT(n), like max(), etc.

Also in the following line, TT(n)/s will have problems because you are dividing a constant by a vector.

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Mark 2013-6-4

在 MATLAB Online 中打开

Are you trying to store TT values for all n, or just the n from 100 until it reaches TT=0.9988s? If it's storage for all n, just run the n loop all the way to 12000 using TT(n,:)=kt*... as the array, and then you can use a loop on the columns of TT to see where TT surpassed 0.9988s in each column:

for col = 1:size(v,2)
nEq(col) = find(TT(:,col)>0.9988*s,1)
end
 The vector nEq will be 11 numbers, giving the values of n that correspond to when TT first was greater than 0.9988s.