MATLAB: Indexing in nested loop

for loopincrementationindexing

Hi,
I have nested loops in a code and I create files that increased for every loop which works like that: data1 gives me the number of lines created in the loop for the para meters 'a' and 'b', data2 gives me for each lines created its orientation/angle.
 for a=1:20
 ...
   for b=1:20
    if
    ...
    data1(a,b)=data1(a,b)+1
    data2(data1(a,b),b)= tan(x/y)
    end
   end
 end
But when I try with non-successive values, it doesn't works.
 for a=1:5:101
 ...
   for b=1:20
    if
    ...
    data1(a(i),b)=data1(a(i),b)+1
    data2(data1(a(i),b),b)= tan(x/y)
    end
   end
 end
I thought I needed to use the index value (i) of 'a' but it doesn't work like that I supposed or I'm making a mistake somewhere.
Looking forward your advices.
Cheers,
n.

Best Answer

You might consider a loop counter or two:
cnt1 = 0;
cnt2 = 0;
for a=1:5:101
   cnt1 = cnt1 + 1;
   for b=1:20
      cnt2 = cnt2 + 1;
      data1(cnt1,cnt2) = ...
   end
 end
Now you can use the counters where you want and the a and b where you want. The alternative is to set your loop variables to integers (say ii and jj), then index into pre-existing vectors a and b (created before the loop). Such as:
a = 1:5:101
b = b=1:20
for ii = 1:length(a)
   for jj = 1:length(b)
      data1(ii,jj) = ... % Now index into a and b.  a(ii),b(jj)
   end
 end
Note that it doesn't really make much sense to index into your loop variables (a and b) as you had it since they are scalar.
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