how to find out wether the array is Hill or not?

Hey,

If I have an array of numbers for example

a=[1,2,2,3,3,4,4,2,-1,-1]

this array has two series: one is an Ascending series of numbers[1,2,2,3,3] , two is a descending series of numbers [4,4,2,-1,-1] an array which contains this two series is caled a Hill.

note: it still can be a descending or ascendings if the numbers in the array are equal

so how can I find out if it a Hill

I tried to use the "For" loops but matlab said that the matrix deminisions are not okay I did mot understand why?

any help please?

thank you,

[Walter Roberson]

hint: imregionalmax()

Answer 1

[the cyclist]

I think this is right, but I have to admit I have not thoroughly checked it:

% Original data
a=[1,2,2,3,3,4,4,2,-1,-1];

% Find difference between consecutive elements
s = diff(a);

% Find the last "uphill" element, and the first "downhill" element
u = find(s>0,1,'last');
d = find(s<0,1,'first');

% Make sure the last uphill element occurs before the first downhill element
is_hill = u<d

The variable is_hill will be true if a is a "hill", and false if not.

[aya qassim]

Thank you it worked.

Answer 2

[Elijah Smith]

This is just the first thing that I thought of:

function res = Is_hill(array)
    %define variables
    res = -1;
    stopVar = 0;
    %for the given array
    for j = 1:(length(array) - 1)
        %is the array rising:
        if array(j) <= array(j + 1)
            %if it is, keep going
            continue;
        else
            %once it stops rising note the element it stopped at:
            stopVar = j;
            %exit the loop:
            break;
        end
    end
    %if it did increase and is now decreasing:
    if stopVar > 1
       %make sure it doesn't increase again (causing a wave not a hill):
       for ii = stopVar:(length(array)-1)
           %if it is decreasing
           if array(ii) >= array(ii + 1)
               %then go check next set of elements:
               continue;
           else
               %if it starts to increase again then it is not a hill
               res = false;
               break;
           end
       end
    else
        %if it never increase or never decrease then it is not a hill:
        res = false;
    end
    %if it's not false it must be true:
    if res ~= false
        res = true;
    elseif res == -1
        %if res hasn't changed, there was an error:
        error("there was an error")
    end
end

You might want to change it to fit your needs.