MATLAB: Set Maximum Limit of Array, but keep Gradients the Same.

arraylimitplot

I have an array Batt_C that contains 527040 values (data set of Watts for each minute throughout a year), ranging from -2.8373e+05 : 2.2426e+06.

I want to set the maximum limit in the array which I can do, at size = 1.3222e+06 using:

Batt_C(Batt_C>size) = Batt_C;

If these are plotted I want the gradients from the original Batt_C to transfer to the limited Batt_C array. I.e. if the values go down on the original, then I want the limited to also show the same downward shape. And then rise again accordingly to the limit.

Best Answer

First, do not use size as a variable name as it will prevent you from using the extremely important size function.

Secondly, the line

Batt_C(Batt_C>size) = Batt_C;

will only succeed if no element of Batt_C is greater than size. Otherwise you'll get a dimension mismatch error. I assume the right hand side is supposed to be size.

Anyway, to answer your question, you'll have to identify each continuous run of values above your limit (henceforth called limit not size). Once you've down that subtract from each run the difference from the first element of the run and the limit.

There are several files on the file exchange that can identify runs, it's fairly easy to implement anyway:

abovelimit = Batt_C(:) > limit;
%get start and ends of runs:
runstarts = find(diff([0; abovelimit]) == 1);
runends = find(diff([abovelimit; 0]) == -1);
%adjust each run:
for run = 1:numel(runstarts)
   Batt_C(runstarts(run):runends(run)) = Batt_C(runstarts(run):runends(run)) - ...
                                         (Batt_C(runstarts(run)) - limit);
end

Related Solutions

MATLAB: Array size goes out of bounds in for loop.

Preallocate! Preallocate! Preallocate! It makes your loops run faster and it avoids this sort of bugs.

What the problem is I suspect: You create or grow your SVD, SVDa and WVD in a loop, without preallocation, which means that a) they end up being row vectors when ideally they should be column vectors and b) their size never gets reset.

So, on the first step of your k987 loop, you end up with alt, PP, temps of a given size, e.g. 8214x1. Because, it's the first time you run your code SVD, SVDa and WVD don't exist and your loop slowly grows them until they are of size 1x8214. Concatenate the transpose and all is well.

Next step of the k987 loop (next excel file), alt, PP and temps are a different smaller size, e.g. 4629x1. SVD, SVDa and WVD and are already of size 8214x1 so your i and jy loop end up filling the first 4629 elements of each. Elements 4630:8214 are still there from the previous loop, so you end trying to concatenate 4629x1 with 8214x1. You get the error.

Had you preallocated SVD, SVDa and WVD, you wouldn't have had that problem. Before the loops:

SVD = zeros(size(alt), 'single');
SVDa = SVD;
WVD = SVD;

which also has the advantage of creating them as column vectors, meaning you don't need the transpose anymore.

Even better, get rid of the useless i and jy loop, create the vectors in one go which then does not need preallocation and ensure they're always the correct size:

SVD = polyval(temps, [1, 8.1847e-3, 0.032321, 5.018 + 3.1243e-4]); %you may have made an error in your original equation which I've not corrected here
SVDa = SVD / 100;
WVD = RH1/100 .* SVDa/1000;

MATLAB: In an array of numbers (0 to 255 of data type uint8), if any number occurs more than 3 times, I would like to insert number ‘255’ (uint8) in between the array and return the position where ‘255’ was inserted. Can somebody please help me

Use diff and strfind (which works with numbers as well) to find your runs. The tricky bit is making sure you don't include the same number in two sequences for sequences longer than 3:

input = [1 255 0 0 0 9 9 9 1 6 6 6 6 6 6 1]
runstarts = strfind(diff(input), [0 0]);
%for sequence of more than 3 it returns indices of overlapping sequence. 
%note that from the wording of your question, I would understand that only
%one number should be returned whatever the length of the sequence, in which case:
%runstarts([false diff(runstarts) < 3]) = []
%takes care of it. But according to your example, you define a new sequence
%after just three repeats, in which case:
posoverlap = find(diff(runstarts) < 3, 1);
while posoverlap
    runstarts(posoverlap + 1) = [];
    posoverlap = find(diff(runstarts) < 3, 1);
end
runends = runstarts + 2;

To insert the 255, I would then convert the array into subarrays using mat2cell and the power of matlab's indexing:

subinput = mat2cell(input, 1, diff([0 runends numel(input)])); %split at the end of each run
subinput(2, :) = {255}; %add a row of 255
subinput(end) = []; %replace last 255 with empty
output = [subinput{:}]; %use indexing + cell expansion to list to reshape into a matrix
outputindex = runends + (1:numel(runends))

Best Answer

Related Solutions

MATLAB: Array size goes out of bounds in for loop.

MATLAB: In an array of numbers (0 to 255 of data type uint8), if any number occurs more than 3 times, I would like to insert number ‘255’ (uint8) in between the array and return the position where ‘255’ was inserted. Can somebody please help me

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