How can I change (or not change) the value of a variable each iteration?

Hi,

I am attempting to either change the value of a variable each iteration, or keep the value the same, depending on the circumstances. I have a loop of 24 iterations,where I am selecting elements from a matrix (X) according to a set of criteria. It is set up something like the following:

X=matrix
xpos=100 %initial x- position
ypos=100 %initial y- position

    for t=1:24
        hour = t
        trip_duration = t

     for ii=1:10
      for jj=1:10
        if X(xpos+ii,ypos+jj) = 0
           trip_duration  = 1
        end
       end
     end
  end

Basically, the variable "trip_duration" resets to "1" every time an element with a value of "0" is found. The idea is for trip duration to then be "2" in the next iteration. If no element with a value of 0 is found, then trip-duration is simply "t". So, at any point in the loop, trip_duration and t can have different values, or the same. I've tried several ways to represent this, but am not successful in having trip_duration increase from it's previous value. For example, I can change the value to "1" during an iteration, and instead of changing to "2" during the next iteration, it will be the value of "t". I've simplified the code a good amount below so please let me know if what I am asking is not clear. Any help is appreciated!

[Stephen23]

@Stephanie Diaz: please edit your question and upload a sample matrix by clicking the paperclip button. Also tell us exactly what you expect the code output to be with that sample matrix.

[Stephanie Diaz]

@Stephen: The matrix that I am using is actually a raster of a landscape, and so it's quite large. Values of "0" correspond to a particular landscape feature. Do I upload a smaller version of the matrix I'm using?

[Stephen23]

@Stephanie Diaz: yes please.

[Walter Roberson]

Note: your code as written,

     for ii=1:10
      for jj=1:10
        if X(xpos+ii,ypos+jj) = 0
           trip_duration  = 1
        end
       end
     end

can be optimized to

if any( any( X(xpos+1:xpos+10, ypos+1:ypos+10) ) )
  trip_duration = 1;
end

[Stephanie Diaz]

@Stephen: I'm not sure how to save a variable within matlab, but the matrix would be a larger version of say X=eye(10).

[Stephanie Diaz]

@Walter: Thanks!

[Walter Roberson]

Correction:

if any( any( ~X(xpos+1:xpos+10, ypos+1:ypos+10) ) )

which is the same as

    if all( all( ~X(xpos+1:xpos+10, ypos+1:ypos+10) ) )

and due to the way MATLAB handles "if" with arrays, that can be further abbreviated to

    if ~X(xpos+1:xpos+10, ypos+1:ypos+10)

but doing so loses some clarity

[Santhana Raj]

does this work for you?

    for t=1:24
        hour = t;

      if any( any( ~X(xpos+1:xpos+10, ypos+1:ypos+10) ) )
           trip_duration=0;
      else
           trip_duration=t;
      end
  end

[Walter Roberson]

The trip_duration=0 should be trip_duration=1 for consistency with the problem requirements.