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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Surabhi A S
Surabhi A S 2022-8-22
评论： Surabhi A S 2022-8-23
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.

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Cris LaPierre
Cris LaPierre 2022-8-22
Ran in:
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
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Cris LaPierre
Cris LaPierre 2022-8-22
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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the cyclist
the cyclist 2022-8-22
Ran in:
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
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the cyclist
the cyclist 2022-8-23
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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