MATLAB function help, input arguments errror

I'm using matlab, and I'm trying to make a function that gives me the probabilities in a geometric distribution when I enter the values of p, q, and no. of attempts(x) as the inputs.

My function:

function Probability = Geometric(p, q, x)

Probability = p*q^x-1

Now whenever I try to calculate the probability by typing in the values of p, q, and x, such as:

geometric(0.5, 0.5, 1),

it gives me an error about "invalid function for input arguments of type double" sort. Can anyone please help me?

I've tried changing functions, and reducing them to one input and one output.

Please help me someone, and if possible, give me a recommendation on how to make a better function. I thought on making one on the binomial distribution, but it would be difficult to get factorials, and get the probabilities to sum up if I need probabilties for multiple succesess.

[Adam Danz]

It would be helpful to have

• the full copy-pasted error message
• all relevant code that defines the function and it's inputs

[Sonny Jordan]

I did provide all the coding to the function and the inputs. The exact error I'm getting is:

??? Undefined function or method 'geometric' for input arguments of type 'double'.

[Adam Danz]

See Steven Lord's answer below. If changing the case from geometric() to Geometric() fixed the problem, please accept his answer.

[Sonny Jordan]

It didn't.

[Adam Danz]

First of all, we need to know which of the two functions you're trying to reference:

1. Geometric()
2. geometric()

Then we need to know where you're storing this function. Is it in it's own m-file with the same exact case-sensitive name? Is that funciton on the matlab path? Is it a nested function?

After we've got answers to those question we can take some additional steps as needed.

[Sonny Jordan]

I honestly don't know what you're talking about. Forget geometric, it's Geometric. I made the function's name Geometric, the file's name is Geometric.m. How do I know the function is on the matlab path and if it's a nested function?

[Adam Danz]

[Adam Danz]

As Steven Lord wrote 30 minuts ago, you're not calling Geometric(); you're calling geometric() which is not the same function. At least that's what you've told us in your question. Maybe it was a typo but we can only work with the info that was given to us.

[Sonny Jordan]

Yes, that was a mistake. I tried doing Geometric as Steven asked me, but it still doesn't work.

Answer 1

[Adam Danz]

After saving your function, add it's path to matlab.

Suppose you saved your function in C:\Users\name\Documents\MATLAB\

addpath('C:\Users\name\Documents\MATLAB\')

Then you should have access to your function.

[Sonny Jordan]

Thanks, it works now. But the function's answer is stuck on -0.5.

I did Geometric(0.5,0.5,1), but it gives me -0.5. If I type just Geometric, it still gives me -0.5. I tried Geometric(0.5,0.5,0), still gives me -0.5. Why's that?

[Adam Danz]

I'd need to look under the hood to speculated. If you want to copy-paste the entire function here I can look at it.

Is this the entire function?

function Probability = Geometric(p, q, x)
         Probability = p*q^x-1; 

When I run that function, with inputs of [0.5, 0.5, 1], I get an output of -0.75.

Furthermore, when you just type 'Geometric', you should get an error "Not enough input arguments".

Clear your workspace and try again.

Answer 2

[Steven Lord]

function Probability = Geometric(p, q, x)

This suggests the name of the function file containing this function is Geometric.m.

geometric(0.5, 0.5, 1),

The function named geometric is not the same as the function named Geometric. Function names in MATLAB are case sensitive.

If changing the case of your call does not resolve the problem, please provide the information Adam Danz requested. Don't paraphrase the error message, copy all the red text directly from the Command Window into the MATLAB Answers comment box.

[Sonny Jordan]

function Probability = Geometric(p,q,x)

p=0.5;

q=0.5;

x=1;

Probability=p*q^x-1;

This is what I have in my function window or editor.

>> geometric(0.5,0.5,1)

??? Undefined function or method 'geometric' for input arguments of type 'double'.

This is what I get in my command window. I did try Geometric, but the error continued.

[Adam Danz]

Ok, so you haven't got a function named Geometric() nor a function named geometric(), is that correct? You can confirm that by running these two lines:

which Geometric
which geometric

[Sonny Jordan]

I did which Geometric, and then which geometric, but it just gave me:

>> which Geometric

'Geometric' not found.

>> which geometric

'geometric' not found.

[Adam Danz]

Ok, this is helpful. So matlab doesn't know the function 'Geometric()' exists. You also mentioned that it's a nested function. Are you calling Geometric() from within the same file that defines this function? Are you calling Geometric() from the command window before the function was created?

[Sonny Jordan]

No, I didn't call Geometric from the command window before the function was created. I started fresh, went over to NEW > Function > Made the Geometric function > Went to Command Window > Geometric(0.5,0.5,0) > Error.

As for this question: Are you calling Geometric() from within the same file that defines this function?

I don't understand, what do you mean?

[Sonny Jordan]

I'm calling Geometric() from the command window, but after I created the function itself.

[Adam Danz]

I thought you mentioned that it was a nested function earlier but I may have misread your comment. So you have a file named 'Geometric.m' and the file is saved and the function within that file has the same name. In that case, it sounds like you just need to add the path to matlab. I've provided an answer to show you how to do that.