I am getting "Array indices must be positive integers or logical values" in my code.

x = 5;
errorThreshold = 0.001;
approximatedCos = 0;
for i = 0:20
    term = ((-1)^i) * (x^(2*i)) / factorial(2*i);
    
    approximatedCos = approximatedCos + term;
    if abs(term) < errorThreshold
        break;
    end
end
fprintf('Approximated cos(%g):%g\n', x, approximatedCos);

I am getting the error in the term = ((-1)^i) * (x^(2*i)) / factorial(2*i); section and I couldn't fix it. Can someone help?

Answer 1

[Voss]

You have created a variable called "factorial", the existence of which prevents you from using the "factorial" function.

Run

clear factorial

and then run your script again.

[Arda]

Thank you for the reminder! Really appreciate it. I guess I didn't see the factorial variable :(

[madhan ravi]

Nice one , Voss. My skills became a litte rusty didn"t see that one. Hopefully I get a laptop soon ;). Answering with phone is really difficult.

[Voss]

@madhan ravi: Thanks!

@Arda: You're welcome!

Probably you created the variable "factorial" in another script (or an older version of this script). Scripts run in the base workspace and operate on variables in the base workspace. All scripts you run share the same workspace (the base workspace). Once a variable is in the base workspace, it stays there until it is cleared (or until MATLAB is restarted).

Functions, on the other hand, each have their own workspace which is created when the function starts running and is cleared when the function exits. That is, (by default) no variables in a function's workspace persist to potentially interfere with the running of another function. So this problem would not have happened if the code had been in a function instead of a script.

[Arda]

Yeah you're right, I was doing another code about factorials and I forgot to clear the previous variable defined to factorial. I don't how missed it but it happens right? Anyways, have a great day!

Answer 2

[Shoresh Shokoohi]

You need to define it yourself or use the factorial function from the MATLAB Statistics and Machine Learning Toolbox.

Here is an example of how you can define the factorial function in your code:

x = 5;

errorThreshold = 0.001;

approximatedCos = 0;

% Define factorial function

fact = @(n) prod(1:n);

for i = 0:20

term = ((-1)^i) * (x^(2*i)) / fact(2*i);

approximatedCos = approximatedCos + term;

if abs(term) < errorThreshold

break;

end

end

fprintf('Approximated cos(%g): %g\n', x, approximatedCos);

[Dyuman Joshi]

"You need to define it yourself or use the factorial function from the MATLAB Statistics and Machine Learning Toolbox."

Why do that when there is a built-in function available?