Matrix with angles that change with each iteration. For loop?

Question

Carlos So 2015-6-15

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/223807-matrix-with-angles-that-change-with-each-iteration-for-loop

评论： Walter Roberson 2015-6-15

I trying to create a plot using a matrix that changes angles from 0 to 180. I have two issues that I can't figure out. 1 How can I make it so my T value changes every time with each angle, and 2.How do I extract specific values from the resultant matrix sigma? I only want all the values in the first row first column and the first row second column in separate values so I can plot them? Maybe I'm approaching this while thing wrong, below is the code I came up with. Any help is highly appreciated.

c

lc; close all; clear all;
sig = [45 30; 30 -60]
for i = 0:180
    T = [cosd(i) sind(i);-sind(i) cosd(i)]
      sigma=T*sig*(T)'
      primesig = sigma(1,1)
      primetau = sigma(1,2)
  end
plot(primesig,primetau)
xlabel('sigma');
ylabel('tau');
title('Stress VS Strain');

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

Walter Roberson 2015-6-15

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/223807-matrix-with-angles-that-change-with-each-iteration-for-loop#answer_182669

在 MATLAB Online 中打开

Your code already uses a different T for each iteration and already extracts sigma values as needed. Your code has a different problem: it overwrites the prime* variables on each iteration. Instead of your code

      primesig = sigma(1,1)
      primetau = sigma(1,2)

you should have

      primesig(i) = sigma(1,1)
      primetau(i) = sigma(1,2)

3 个评论
显示 1更早的评论隐藏 1更早的评论

Walter Roberson 2015-6-15

在 MATLAB Online 中打开

      primesig(i+1) = sigma(1,1)
      primetau(i+1) = sigma(1,2)

Walter Roberson 2015-6-15

在 MATLAB Online 中打开

More generally when you have a list of values that you want to go through, then a useful technique is to assign the list to a variable and step through the variable:

ivals = 0:180;                %put values in variable
for K = 1 : length(ivals)     %iterate over indices of variable
  i = ivals(K);               %retrieve the value for this iteration
    T = [cosd(i) sind(i);-sind(i) cosd(i)];
    sigma=T*sig*(T)';
    primesig(K) = sigma(1,1);   %store relative to loop count
    primetau(K) = sigma(1,2);   %store relative to loop count
  end