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Check if all previous array values meet a condition

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Ikenna Okoye
Ikenna Okoye 2020-5-18
评论： Walter Roberson 2020-5-19
Hi all, I have a problem where im trying to access all previously genereated values in a for loop. These values are all being stored in an array. How would I then check if the current object is less then (or any condition) all of the previous array values. If anyone has an idea of how to do this, it would be of great help, thanks.

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Walter Roberson
Walter Roberson 2020-5-18
编辑：Walter Roberson 2020-5-18
%instantaneous, but values could be in any order
tf = A(idx) < min(A(1:idx-1))
%is it true that every value is less than the previous?
tf = all(diff(A(1:idx)) < 0)
%is it true that every value up to some point is less than some constant
tf_vector = cumprod(A < constant);
first_not = sum(tv_vector) + 1;
  2 个评论
Ikenna Okoye
Ikenna Okoye 2020-5-19
Hi Walter, just a few questions. What does 'idx' represent and is 'A' equal to the array that wlll be iterated through to check the coditions? It aslo seems that he three steps you have outlined would be how you are going through the problem? For my problem, i'm not sure if step 2 would be necessary, though i could be wrong.
Walter Roberson
Walter Roberson 2020-5-19
idx is the index of the "current object" -- the location to be compared to previous objects.
A is the array being checked against.
The three sections there are in response to three different possible needs.
The first section is for the case where you do not care what order the previous entries are in and just need to know that the current entry is less than any of what went before.
The second section is for the case where values need to be strictly decreasing and you want to verify that for some particular location.
The third section is for the case where what you want to know is the first location that is not less than a particular value. It is equivalent to
first_not = length(A)+1;
for idx = 1 : length(A)
if ~(A(idx) < constant)
first_not = idx;
break;
end
end

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