Using vector as range in for-loop In Matlab

Question

I was wondering what the rule is for using vectors as range in for-loop in Matlab?

For example,

range = [0.1:0.01:2]'; % wrong
range = [0.1:0.01:2]; % correct

for i = range
i
end

Why is it that if range is column vector, it will not work, while if range is row vector, it will?
Will i = range be interpreted as i taking each value of range, or i is assigned with vector range?

Thanks~

Sam Roberts · Accepted Answer · 2012-05-14 15:13:03Z

11

More generally, range can be a matrix, and the loop variable loops over its columns.

range = rand(3,3);
for col = range
col
end

col =
      0.86341
      0.11625
      0.20319
col =
      0.59721
     0.098357
       0.8356
col =
      0.89578
      0.46217
      0.93585

So if range is a row vector, it will loop over its values. But if range is a column vector, it will loop over that single column as its value.

answered May 14, 2012 at 15:13

Sam Roberts

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Oliver Charlesworth · Accepted Answer · 2012-05-14 14:52:00Z

3

From http://www.mathworks.co.uk/help/techdoc/ref/for.html:

for index = values
   program statements
          :
end
... values has one of the following forms:

valArray

creates a column vector index from subsequent columns of array valArray on each iteration. For example, on the first iteration, index = valArray(:,1)...

answered May 14, 2012 at 14:52

Oliver Charlesworth

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High Performance Mark · Accepted Answer · 2012-05-14 15:08:16Z

0

It's that way because it's that way. I don't think that there is any deep explanation for this.
As you would discover if you experimented, once you've made an assignment such as range = [0.1:0.01:2] then the variable called range is a row-vector comprising the values in the range. Your loop will work just fine. As it would if it started

for i = [0.1 0.11 0.12 ...]

edited May 14, 2012 at 15:08

answered May 14, 2012 at 14:52

High Performance Mark

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