I want to get the difference between the present number and the previous number for 1000 set of data from the plot.

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For example,
I have considered 10 random values from the set of 1000 values
X-axis values are as given a = [ -9.658 -9.321 -8.979 -8.742 -8.247 -7.291 -6.738 -7.439 -8.733 -8.596 ]
Y-axis values are as given b = [134 135 136 137 138 139 140 141 142 143 ]
I want to consider each set of values and find the difference between the number and its previous number for example a2-a1,a3-a2,a4-a3.... till a1000-a999. Depending upon these values if its increasing(difference is positive) or decreasing(difference is negative) or constant(difference is zero) I have to find out the threshold value of the given set. Please help me with the code.

Accepted Answer

Cris LaPierre
Cris LaPierre on 22 Aug 2022
Do you mean a2-a1,a3-a2,a4-a3,...., a1000-a999?
If so, use the diff function.
a = [ -9.658 -9.321 -8.979 -8.742 -8.247 -7.291 -6.738 -7.439 -8.733 -8.596 ];
c=diff(a)
c = 1×9
0.3370 0.3420 0.2370 0.4950 0.9560 0.5530 -0.7010 -1.2940 0.1370
  3 Comments
Cris LaPierre
Cris LaPierre on 22 Aug 2022
I don't understand why you need a while loop to do that. Diff uses exactly the formula you wrote.
Y = diff(X) calculates differences between adjacent elements of X along the first array dimension whose size does not equal 1:
  • If X is a vector of length m, then Y = diff(X) returns a vector of length m-1. The elements of Y are the differences between adjacent elements of X.
Y = [X(2)-X(1) X(3)-X(2) ... X(m)-X(m-1)]

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More Answers (1)

the cyclist
the cyclist on 22 Aug 2022
a = [2 3 5 7 11];
a - a' % All possible differences between pairs of elements of a
ans = 5×5
0 1 3 5 9 -1 0 2 4 8 -3 -2 0 2 6 -5 -4 -2 0 4 -9 -8 -6 -4 0
  7 Comments
the cyclist
the cyclist on 23 Aug 2022
OK. As you figured out, I guess, @Cris LaPierre's answer does exactly that.
I'm confused by your original question, though, which stated that you also needed non-consecutive differences, such as a(4) - a(1) = 5.
But, I'm glad you got it solved.

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