Problem with array filling

Hi,

I need to do this:

for i=0.1:0.1:360
j(i*10)=2;
end

but I obtain this error message:

??? Attempted to access j(3); index must be a positive integer or
logical.

Could you help me?

Thanks in advance

Thomas

Answer 1

[Image Analyst]

Besides the others all saying to cast your index to integer like this:

for k = 0.1 : 0.1 : 360
  jArray1(int32(k * 10)) = int32(2);
end

I also want to say that it's usually recommended not to use i and j (though you can) as variable names since they also are the imaginary variable. Hence my new names in the corrected code above.

Also, there are some other ways that are more probably efficient and "MATLAB-ish" to do what you did, such as the methods below:

jArray2 = 2 * ones(1, 3600, 'int32');
jArray3(1 : 3600) = int32(2);

Answer 2

[Oleg Komarov]

sprintf('%.17g', 0.3)
ans =
0.29999999999999999

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

Answer 3

[Matt Fig]

The reason you get this error is because of floating point arithmetic.

Look closely:

isequal((0.1:0.1:1)*10,1:10)  % NO!

Here is the closer look:

x = (0.1:0.1:1)*10;
x==(1:10) % Notice the third return is a zero, here's why:
fprintf('%.16f\n%.16f\n',x(3),3) % Print out and compare...

Answer 4

[Azzi Abdelmalek]

in matlab index must be a real strict positiv integer

it does'nt accept x(0) or x(-1)

 h=zeros(360*10/0.1,1)
 for j=0.1:0.1:360 
 ind=int16(j*10)  % convert to integer, for biger number, u can use int32, int64
 h(ind)=2; 
 end

Answer 5

[thomas82]

Thank you for your answers, now I understood and resolved! Thomas