Storing vectors from a for loop, into a 2d matrix.

Greetings all,

Hopefully this is a relatively trivial issue, i have observed this short for loop:

>> for r = 1 : 10 vec = [10:20]+r mat(r,1) = vec end

which creates 10 vectors, e.g:

11 12 13 14 15 16 17 18 19 20 21

and stores them in a matrix like this:

11    12    13    14    15    16    17    18    19    20    21
12    13    14    15    16    17    18    19    20    21    22
13    14    15    16    17    18    19    20    21    22    23 ....etc

When i am trying to utilise this for my own project, i need it to be of the form:

for r = 1 : 5 : 16 vec = [10:20]+r mat(r,:) = vec end

which i thought would give:

11 12 13 14 15 16 17 18 19 20 21

16 17 18 19 20 21 22 23 24 25 26 etc.

But i am getting:

    11    12    13    14    15    16    17    18    19    20    21
     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0
    16    17    18    19    20    21    22    23    24    25    26
     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0     0

Where do all these 0's erupt from? i must plot the array without the zero's because my actual data is much larger (approx for k = 1: 500: 1000000) and exponential number of 0's just exceeds matlab capabilities.

anyone know a better way of storing these results in a 2d array? thank you, much obliged.

David

Answer 1

[Sean de Wolski]

Well when r = 1: you index into

mat(r<:)

But then the next iteration r = 6 and you have:

mat(r,:)

So you need to keep a counter:

cnt = 0;
for r = 1:5:16
  cnt = cnt+1;
  mat(cnt,:) = whatever
end

[David Mehr]

/this is just what i needed, a simple and practical solution. Very grateful for this. I'm very new to MATLAB (and programming in general) but this really helps me get on with my studies. Thank you! :D