Subtracting elements within constraints

Hi all,

I have a vector and I subtract each element from the previous one using the cumsum function like this

 B = bsxfun(@minus, A(1,:), cumsum(A(2:end,:)));

However, the values should be within some particular range (min=1.3 and max=11.7).

So I used this command:

 B = max(1.3, min(11.7,(B));

The results before and after the constraint are:

8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.896388843  8.896388843
8.899933525  8.899933525
8.899933525  8.899933525
9.315786868  9.315786868
9.743121832  9.743121832
10.41242251  10.41242251
10.8175055  10.8175055
10.83527583  10.83527583
10.84671199  10.84671199
10.92675208  10.92675208
11.31588974  11.31588974
11.7          11.7
11.7          11.7
11.7          11.7
11.74200832  11.7
11.98760913  11.7
12.63688627  11.7
13.29973854  11.7
14.17196338  11.7
14.57395341  11.7
15.06132339  11.7
14.64806384  11.7
14.65909789  11.7
14.67088601  11.7
14.39082286  11.7
13.95882417  11.7
13.52282417  11.7
13.09282417  11.7
12.54482417  11.7
12.00682417  11.7
11.52282417  11.52282417
11.01882417  11.01882417

My problem is that When the value in the vector goes up I dont have a problem as I get the maximum value. However, when the vector start decreasing I want something different:

    15.06132339  11.7
    14.64806384  11.7 (I want the value 11.7-(15.06132339-14.64806384)= 11.27

Same thing for all the values when decreasing

is there any way to do this?

I don't know if you get my question

thanks anyway!

Answer 1

[Image Analyst]

Use diff() to find out where the result is negative. When it's negative, the array is decreasing.

differences = diff(B);
decreasingIndexes = differences < 0;
B(decreasingIndexes) = .........

[Nikolas Spiliopoulos]

thanks for the answer, however I don't really get it how will be the last command. Moreover, I need to do this only when the maximum limit has been reached. I have an Array instead of a vector, so many times the maximum limit is not reached. I still don't get it how to do it thanks!

Answer 2

[Jan]

I do not understand: "I subtract each element from the previous one using the cumsum function". Actually diff(A) should do this, or the equivalent A(2:end) - A(1:end-1). But where does the cumsum come from?

It is not clear to me how

15.06132339  11.7
14.64806384  11.7 (I want the value 11.7-(15.06132339-14.64806384)= 11.27

must be generelized for the other elements. Please explain again the procedure to get the results starting from "A" and not from "B".

[Nikolas Spiliopoulos]

thanks for the answer, actually It subtracts the second element from the first and holds the result. Then the next element is subtracted from the previous result and so on. that's why I am using cumsum.

However, I have an array 48X365, and I do this for each column within min-max range. Diff(A) Gives A diff answer:

if true
  example:
A=
1.30000000000000       
-0.447611319007917
-0.00239052668507496
0.00222517216126071
0.121515280554814
0.258000000000000
0.148000000000000
0.101000000000000
0.133000000000000
0.260000000000000
0.974000000000000
2.03500000000000
1.44000000000000
0.868000000000000
0.575000000000000
0.459000000000000
0.707000000000000
0.392000000000000
0.382000000000000
end

if true
  with cumsum
1.74761131900792
1.75000184569299
1.74777667353173
1.62626139297692
1.36826139297692
1.22026139297692
1.11926139297692
0.986261392976917
0.726261392976917
-0.247738607023083
-2.28273860702308
-3.72273860702308
-4.59073860702308
-5.16573860702308
-5.62473860702308
-6.33173860702308
-6.72373860702308
-7.10573860702308

with Diff(A)

   -1.7476
    0.4452
    0.0046
    0.1193
    0.1365
   -0.1100
   -0.0470
    0.0320
    0.1270
    0.7140
    1.0610
   -0.5950
   -0.5720
   -0.2930
   -0.1160
    0.2480
   -0.3150
   -0.0100

end

[Nikolas Spiliopoulos]

The elements are positive and negative, so the the value can be decreased or increased!