Problem with array filling
显示 更早的评论
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
采纳的回答
Image Analyst
2012-8-17
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);
更多回答（4 个）
Oleg Komarov
2012-8-17
编辑：Oleg Komarov
2012-8-17
sprintf('%.17g', 0.3)
ans =
0.29999999999999999
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...
Azzi Abdelmalek
2012-8-17
编辑：Azzi Abdelmalek
2012-8-17
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
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