Code for Monotonically increasing function

Hi All,

Can anyone check the following code snippet and tell me why it fails for the following test cases?

x = cumsum(rand(1,100));
x= [ -3 -2 -1 0 1 2 3]
function tf = mono_increase(x)
  for ii=1:length(x)
      for jj=(ii+1):length(x)
          if x(ii)<x(jj)
              tf = true;
          else 
              tf = false;
          end
      end
  end
end

I'm getting the desired result in my laptop but with the compiler of MATLAB , I'm getting error.

Please someone tell me how to resolve it.

[Stephen23]

"I'm getting the desired result in my laptop ..."

I doubt that.

Your code simply overwrites tf on every loop iteration, which is unlikely to give the required result (if the goal is to test that all values are monotonically increasing). You will need to use some logical operation or indexing or something similar to check that all pairs of values fulfill the required condition/s. Two loops is unlikely to be useful, one is enough.

Or you could just use the simple MATLAB approach using diff and one logical comparison.

[Swati Sarangi]

@Stephen

With one loop , will not there be an out-of-bound error?

[Stephen23]

"With one loop , will not there be an out-of-bound error?"

Not if the loop iterates the correct number of times (hint: one less than the number of elements).

Answer 1

[KSSV]

x= [ -3 -2 -1 0 1 2 3] ;
function tf = mono_increase(x)
tf = 1 ; 
for i = 1:length(x)-1
  if x(i+1) < x(i)
    tf = 0 ;
    break
  end 
end
end