indexing in nested loop
显示 更早的评论
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.
采纳的回答
Matt Fig
2011-4-14
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.
更多回答（1 个）
Robert Cumming
2011-4-13
in your first example in each loop a is:
1 2 3 4 5 6 7 8 9 10 11 ... 20
In your second it is:
1 6 11 16 21 26 31 .... 101
what were you expecting a(i) to do? If your confused on the value of a in each loop - print it to the screen (or check in the debug)
The answer to this question will depend on what you want to do with your data variables.
类别
在 帮助中心 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
