index out of bounds error

Hey all, my code looks something like this.

clear
clc
x = -10:0.1:10;
f1 = trapmf(x,[-2 0 0 2]);
f2 = trapmf(x,[1 3 3 5]);
kvals = 0.05:0.05:1;
for kidx = 1 : length(kvals)
  k = kvals(kidx);
  index1 = find(abs(f1-k)<10^(-10));
  Xidx1{kidx} = x(index1);
  Xidx1{20} = [0 0];
  index2 = find(abs(f2-k)<10^(-10));
  Xidx2{kidx} = x(index2);
  Xidx2{20} = [0 0];
  A(kidx) = Xidx1{kidx}(1);
  B(kidx) = Xidx1{kidx}(2);
  C(kidx) = Xidx2{kidx}(1);
  D(kidx) = Xidx2{kidx}(2);
end

It works perfectly for what it is, getting lower and upper bounds of my functions f1 and f2.

But for some reason if I change my f1 or f2 functions to something else, I am getting a number of elements error?

Like f2 = trapmf(x,[1 3 3 4])

will give me an error, and I can't seem to figure out why that is?

the exact error message is

Attempted to access Xidx2.%cell(2); index out of bounds because

numel(Xidx2.%cell)=1.

Error in (line 22)

D(kidx) = Xidx2{kidx}(2);

Answer 1

[Brendan Hamm]

You are using the find function and then assigning values based on that to the variable Xidx2{kidx}. If you use the debugger with the change you mentioned you will notice that on the first run there is exactly one return value for the line:

index2 = find(abs(f2-k)<10^(-10));

Therefore the value being passed in the following assignment is a scalar:

Xidx2{kidx} = x(index2);

Therefore you get an error in the indexing that follows:

D(kidx) = Xidx2{kidx}(2);

There is nothing in this code which will guarantee that there are multiple values which satisfy the inequality:

abs(f2-k)<10^(-10)

You could use an if statement or try-catch block to perform this check for you.

When you encounter these errors, use the debugger , it is your friend.