Subscript indices must either be real positive integers or logicals.

dear all

i have code like below

clc
clear all 
for b=1:0.1:20
    M((b*10)-9,:)=[1 1 1 ]
end

but at b=2.4 i got this error :

M =

     1     1     1
     1     1     1
     1     1     1
     1     1     1
     1     1     1
     1     1     1
     1     1     1
     1     1     1
     1     1     1
     1     1     1
     1     1     1
     1     1     1
     1     1     1
     1     1     1

Subscript indices must either be real positive integers
or logicals.

Error in Untitled2 (line 4)
    M((b*10)-9,:)=[1 1 1 ]

i really appreciated if some can help me y i get this error and what the solotions ?

[Adam]

Why are you using such complex maths for your indices? If you really must do that then use

doc round

e.g.

M( round( (b*10)-9 ), : ) = [1 1 1];

Floating point numbers are not perfectly represented so when you start doing maths with them which, in theory, should result in an integer value in practice does not due to rounding errors caused by how floating point numbers are represented on a computer.

[Stephen23]

"i really appreciated if some can help me y i get this error..."

https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero

"...and what the solotions ?"

Do not do calculations on floating point numbers and expect to get exact integer outputs. Write your code knowing that calculations on floating point numbers accumulate floating point error.

[shahin hashemi]

thank you very much

i use round and got answer

u cooment so i cant accept your answer

Answer 1

[Stephen23]

Better to iterate over integer indices rather than fractional values:

V = 1:0.1:20;
N = numel(V);
M = nan(N,3);
for k = 1:N
    M(k,:) = [1,1,1];
end

Even better:

M = repmat([1,1,1],N,1)

Best:

M = ones(N,3)