How to check monotonity of a vector?

How to check easily that components of a vector form a monotone (increasing) sequence or not?

[Adam]

You can use

validateattributes( yourVector, { 'numeric' }, { 'vector', 'increasing' } )

if you just want to validate that it is monotonic and carry on with the code if it is while throwing an error otherwise.

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/matlab/ref/issorted.html

issorted() with 'ascend' (repeats permitted) or 'strictascend' (repeats not permitted)

Answer 2

[KL]

use diff

https://www.mathworks.com/help/matlab/ref/diff.html

along with all maybe

 a = 1:10;
 isIncreasing = all(diff(a)) %or all(diff(a)>=0) if you want to allow 0 difference

[Andreas]

Take care, that all is also true for negative values.

Therefore, this example has a false positive on b

a = [1:10];
b = [1 2 3 2 1 5];

isIncreasingA = all(diff(a)) 

isIncreasingA = logical
   1

isIncreasingB = all(diff(b)) 

isIncreasingB = logical
   1

To fix that, restrict to positive values of diff

isIncreasingA = all(diff(a)>0) 

isIncreasingA = logical
   1

isIncreasingb = all(diff(b)>0) 

isIncreasingb = logical
   0