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

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.

Answer 1

[Cris LaPierre]

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

[Surabhi A S]

Thank you for the answer. But I need help in a code using while loop so that I can iterate directly for 1000 values in excel sheet.

Formula can be y(n) = a(n)-a(n-1) which i have to iterate for 1000 values from a1 to a1000.

[Cris LaPierre]

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)]

[Surabhi A S]

Thank you

Answer 2

[the cyclist]

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

[Surabhi A S]

Thank you for the answer. But I need help in a code using while loop so that I can iterate directly for 1000 values in excel sheet.

Formula can be y(n) = a(n)-a(n-1) which i have to iterate for 1000 values from a1 to a1000.

[the cyclist]

I don't think you have fully understood my solution, maybe because I used an example with only 5 values. But, notice that for n=5, the above-diagonal values are all possible differences

a(2)-a(1) = 1

a(3)-a(1) = 3

...

...

a(3)-a(2) = 2

You could also have done

a = rand(1,1000); % Your data
out = a - a'; % All possible differences

You do not need a while loop. It is easy to store 1,000,000 values in MATLAB.

[Surabhi A S]

What if I dont require a matrix of values and I only require the output values

[the cyclist]

Suppose your input were

a = [2 3 5 7 11]; % Just 5 values, instead of your 1000

What specifically do you want the output to be?

[Surabhi A S]

I want the output to be [1 2 2 4]

[the cyclist]

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.

[Surabhi A S]

Oh sorry. I'm sorry for that, I typed it by mistake.

Thank you for the help