"For colon operator with char operands, first and last operands must be char." error?

for n=1:1:4
    MAT((a:(a+b)),n)=1;
end

a and b are integer numbers that change on each iteration of n

The code is meant to set some zeros in a zero matrix to 1

On the 2nd iteration, i.e. n=2, I keep getting the following error:

"For colon operator with char operands, first and last operands must be char."

[laurie]

% OPTIONS.popsize=4;
% horizon = 6;
% num_gen = 4;
%Population(pop).chrom = structure 'Population' with a cell 'chrom'
% chrom = 1x4 matrix 
%Data is also a struct

for pop=1:1:OPTIONS.popsize
    Population(pop).chrom2 = zeros(horizon,num_gen);

for n=1:1:num_gen    

    a=Population(pop).chrom(1,n);
    b=Data.tend(n)-Data.tstart(n)-1;
    c=a:(a+b)

    %Population(pop).chrom2((a:(a+b)),n)=1;
    Population(pop).chrom2(c,n)=1;

end
end

Answer 1

[Guillaume]

According to the error message, a and b are integer numbers is not true. I suspect that a is actually of type char and b may be integer, which would result in a+b being integer.

Without knowing more about a and b, it's hard to help you, so post the code that generate them.

You can check the type of a and b when you get the error by writing

dbstop if error

at the comment prompt before running your loop / program. Matlab will break into the debugger when it encounters the error. At which point you can issue

whos a b

to see their type.

[laurie]

You're right!

a = char

b = double

I've attached the code to my question

[laurie]

Thank you very much! I've managed to fix the problem.

[Guillaume]

What is the output of

chrom = Population(pop).chrom
whos chrom

when the error occurs? Because that's the source of your problem. Somewhere, you've got a string.

[laurie]

The output was a char, which came from a previous function I created.