Why does this loop create a horizontal array instead of a vertical array?

I know this may seem a really simple question but I just can't seem to work this one out when consulting the manual.

Within my code I have the following loop to work out the difference between sensor readings:

for i = 1 : size(xVal)    
   df([i]) = yVal(i+1) - yVal(i);
End

xVal is a line number and yVal is a sensor reading.

But for some reason, rather than creating a vertical array of difference values, a horizontal array is created and before it is complete MATLAB throws up an error stating "Index exceeds matrix dimensions" (I assume this error is because the horizontal array goes beyond a value MATLAB can handle.)

How can I change this loop so that a vertical array is created? (I also assume that this would overcome the "Index exceeds matrix dimensions" error?)

Any help is greatly appreciated.

Answer 1

[Alexandra]

Why don't you try it with the function diff? It's easier and very quickly...

[Alexandra]

Also you have to put the right dimension when you use size function, especially on a for

for i = 1 : size(xVal,1) % -> Rows

[Red Beard]

This is exactly what I have been looking for. I couldn't find this function in the manual!!!

Thank you.

Answer 2

[Sachin Ganjare]

Probably you have preallocated array df as maybe zeros(x,1). It should be:

   df = zeros(1,x);

x is number of elements in array df

Hope it helps!!!