Length command giving rise to array indices must be positive integers or logical values error

Dear all

I am currently performing some nested loops, as it can be seen here

As you can see I get an error in line 150, but that happens once I have gone through that loop for dx=1 and dy=2.

I do not really understand why, after going through the for loop in line 150 for dx=1 and dy=1, I can not ask anymore for the length of Cr_atoms variable. When I get that error, Cr_atoms variable looks like

basically the same before beginning the nest for loops that begin in line 148.

Any ideas on what it is happening?

Answer 1

[Walter Roberson]

You start out by using the length() function call. But then you assign something to length(1) . That makes length into a variable. Then the next time that what appears to be the length function call is used, instead it is a reference to the length variable.

Answer 2

[Voss]

The code creates a variable called "length" when this line executes:

length(1)=Cr_atoms(i,1)+dx*a; % Angstroms

Any subsequent reference to "length" will now refer to the variable "length" and not the function "length", so on the next iteration of the for dy=1:cells_b loop, when

for i=1:length(Cr_atoms(:,1))

is encountered, length(Cr_atoms(:,1)) is interpreted as a request to index the variable length with indices Cr_atoms(:,1), but since Cr_atoms(:,1) contains numbers other than positive integers, an error is thrown.

You should rename your variable "length" to something else that's not also the name of a function.

Also note that you don't need to use the "length" function at all for this, since length(Cr_atoms(:,1)) is equivalent to size(Cr_atoms,1) (assuming Cr_atoms has at least one column).