While loop to detect 0 slope

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Neil
Neil 2014-6-4
评论： Star Strider 2014-6-4
Hello everyone,
so I'm currently trying to make a code that will separate some data. To do so, I came up with a code that I thought would work, and I've tried looking at the what the error message mean, but I cant understand. My code is the follwoing
*g=0; j=0; A=[5 5]; h=0; slope=5; while (g<1785) & (A(1,1)>0) & (h<0.15) h = AverageStrain(1+g:20+g,:); i = AverageStress(1+g:20+g,:); A = polyfit(h,i,1); j = g+10; g = g+20; end
Cycle1UpStrain=AverageStrain(0:j,1);*
The error message i receive is ;
*Subscript indices must either be real positive integers or logicals.
Error in MTSAnalyser (line 43) Cycle1UpStrain=AverageStrain(0:j,1);*
here, the files AverageStress and AverageStraain are 1785x1 variables. I tried doing a linear fit of 20 data points at the time so that when the linear slope calculated is 0 are negative, it stops and extracts the number j.
j would be used to create a variable made of a fraction of AverageStress and AverageStrain, data points 1 to j. (afterwards I would make it something like j to a new variable limit)
Also, my value of A always ends in something like [574, -64], which is weird since I wanted it to stop at a slope equal 0 or smaller, which is the first row, first column of A.
I'm quite new to Matlab, so try not to assume I know a whole bunch.
Thank you for your help! N
  1 个评论
Star Strider
Star Strider 2014-6-4
Formatted code:
g=0;
j=0;
A=[5 5];
h=0;
slope=5;
while (g<1785) & (A(1,1)>0) & (h<0.15)
h = AverageStrain(1+g:20+g,:);
i = AverageStress(1+g:20+g,:);
A = polyfit(h,i,1);
j = g+10;
g = g+20;
end

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采纳的回答

Star Strider
Star Strider 2014-6-4
Here’s the problem:
Cycle1UpStrain=AverageStrain(0:j,1);
Zero is not a positive integer. Your (variable or index) ‘j’ is also defined as zero, as best I can see from your code (difficult to read because it’s not formatted).
If you want to find the indices where AverageStrain is equal to zero and one respectively, try this:
AvStn0Idx = find(AverageStrain == 0);
AvStn1Idx = find(AverageStrain == 1);
  2 个评论
Neil
Neil 2014-6-4
Thanks, the mistake was in fact the 0 there. it needed to start at 1. Meanwhile, my A still ends at a value of [571, -644]. Ideas?
Star Strider
Star Strider 2014-6-4
I’m not entirely understand what you’re doing, but I see some problems. One is that h is a vector, not a scalar (at least as I read your code), so if any value of h is less than 0.15, that test will be true.
Consider:
h = [0.1 randi(10,1,5)];
htest = h < 0.15
yields:
htest =
1 0 0 0 0 0
You may want to consider how you’re testing h. What information do you really want from it? First value? Last value? Mean? Norm? Minimum? Maximum?
I would solve the h problem (if it is a problem) first, then see if your while loop runs as it should.

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