Nested loop error help

Hello!

I guess this should be super obvious and simple for almost everyone...but for some reason I can't make this nested for loop to work:

I get this error and I'm not sure why: Attempted to access b(1,7); index must be a positive integer or logical.

b = zeros(51,11);

for i = 0:0.01:0.5
  for j = 0:0.1:1
      a = (2*i)+j;
      p = (j/0.1)+1;
      q = (i/0.01)+1;
      b(q,p)= a;
    end
end

Thanks!

Answer 1

[Azzi Abdelmalek]

EDIT

b = zeros(51,11);
for i = 0:0.01:0.5
for j = 0:0.1:1
    a = (2*i)+j;
    p = round((j/0.1)+1);
    q = round((i/0.01)+1);
    b(q,p)= a;
  end
end

[Image Analyst]

Amir, be aware, fix() truncates the fractional part so that if you're just slightly under the integer number, you'll go down one whole integer. that's why I used int32(), which is a rounding like you're familiar with followed by a cast to an integer class. See this demo code:

p=[1.01, 2.99999]
fp = fix(p)
rp = int32(p)

p =  1.01   2.99999
fp =  1     2
rp =  1     3

That's why I suggested int32() instead of fix() in my naswer.

[Amir Alansari]

Thanks a lot that solved my problem!

I still couldn't figure out why I was having the problem, based on the "Walter link" below..but int32 seems to work fine for me.

[Azzi Abdelmalek]

Using fix is a bad idea, you can replace it with round

Answer 2

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

Answer 3

[Image Analyst]

Try this:

b = zeros(51,11);
for i = 0:0.01:0.5
  for j = 0:0.1:1
      a = (2*i)+j;
      p = int32(10*j+1);
      q = int32(100*i+1);
      b(q,p)= a;
    end
end