I need help with fixing the error in my for loop equation

Question

Fun Dan 2015-4-7

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/196586-i-need-help-with-fixing-the-error-in-my-for-loop-equation

评论： Image Analyst 2015-4-8

Please how do I fix the error message: Attempted to access ID(3); index out of bounds because numel(ID)=2.

I am trying to get a sum of all the iteration (H) from the code below: The error is somewhere in the formula for H but I am not able to fix it.

   i=              input('Number of Layers = ');     % Say i=4
  for n=1:i
   ID(n)=          input(['Layer ' , num2str(n) , ' Internal Diameter (m)= ']);
   OD(n)=          input(['Layer ' , num2str(n) , ' Outer Diameter (m)= ']);
   k_L(n)=         input(['Thermal Conductivity of Layer ' , num2str(i) , '(W/(m*K))=  ']);
   *H=   ID(1)*sum((log(ID(n+1)/ID(n))/(2*k_L(n))))* ;  
                                               %D(1) is the innermost pipe layer which is ID at n=1
  end

The formula for H is given below.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Image Analyst 2015-4-7

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/196586-i-need-help-with-fixing-the-error-in-my-for-loop-equation#answer_174360

When you're on the n'th iteration of your loop, why do you think ID(n+1) will have a value yet? You have not assigned a value to that element yet - it's the next one. You won't get the user to specify a value for it until the next iteration.

3 个评论
显示 1更早的评论隐藏 1更早的评论

Image Analyst 2015-4-7

在 MATLAB Online 中打开

If this is homework, make sure you "Tag" it as homework above.

What does the sum go over? If i (which would be better named numberOfLayers) is 4, then does n in the sum go from 1 to 3, so that ID(n+1) will finish at ID(4) and not ID(5) which does not exist?

Alright, let's get you a little closer. Try this code:

numberOfLayers = input('Number of Layers = ');     % Say i=4
for n = 1 : numberOfLayers
  % Create prompts
  prompt1 = sprintf('Layer #%d Internal Diameter (m) = ', n);
  prompt2 = sprintf('Layer #%d  Outer Diameter (m) = ', n);
  prompt3 = sprintf('Thermal Conductivity of Layer %d (W/(m*K)) =  ', n);
  % Ask user for three floating point numbers.
  defaultValue = {'1', '2', '3'};
  titleBar = 'Enter the values';
  userPrompt = {prompt1, prompt2, prompt3};
  caUserInput = inputdlg(userPrompt, titleBar, 1, defaultValue);
  if isempty(caUserInput),break,end; % Bail out if they clicked Cancel.
  % Convert to floating point from string.
  ID(n) = str2double(caUserInput{1})
  OD(n) = str2double(caUserInput{2})  % Not used!!!!!!!
  k_L(n) = str2double(caUserInput{3})
end
% Compute H
ratios = ID(2:numberOfLayers) ./ ID(1 : (numberOfLayers-1))
theFormula = log(ratios) ./ (2*k_L(n))
% Not sure the formula for H is correct since
% it refers to ID*, not ID(1)*, but anyway....
H = ID(1) * theFormula
% ID(1) is the innermost pipe layer which is ID at n=1

I was wondering why your k_L always asked for the value for the last layer - the i'th layer, instead of the n'th layer. Is this just a typo because you did not use descriptive enough variable names? I also don't quite understand that H seems to want the whole ID array multiplied by the sum, which would give another array, rather than ID(1) multiplied by the sum, which is what you did in your code.

Fun Dan 2015-4-8

Thank you very much. It worked great!

Image Analyst 2015-4-8

You're welcome. If we're done here, then can you go ahead and mark my answer as "Accepted"?

请先登录，再进行评论。

Answer 2

Jos (10584) 2015-4-7

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/196586-i-need-help-with-fixing-the-error-in-my-for-loop-equation#answer_174359

在 MATLAB Online 中打开

You want to put the formula for H out of the loop

for ..
  % ask for values here
end
% summing formula here

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Fun Dan 2015-4-7

Hi Jos,

I tried it that way already and it is still giving me the same error message.

请先登录，再进行评论。

I need help with fixing the error in my for loop equation

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

采纳的回答

3 个评论
显示 1更早的评论隐藏 1更早的评论

更多回答（1 个）

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

另请参阅

类别

标签

Community Treasure Hunt

I need help with fixing the error in my for loop equation

0 个评论 显示 -2更早的评论隐藏 -2更早的评论

采纳的回答

3 个评论 显示 1更早的评论隐藏 1更早的评论

更多回答（1 个）

1 个评论 显示 -1更早的评论隐藏 -1更早的评论

另请参阅

类别

标签

Community Treasure Hunt

WeChat

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

3 个评论
显示 1更早的评论隐藏 1更早的评论

1 个评论
显示 -1更早的评论隐藏 -1更早的评论