Access matrix values inside of a function

Hi MATLAB-Folks,

I'm asking with a beginner problem for your help, I searched the forum for an answer but without sucess:

I have a script, that creates a vector, lets say as an example:

>> g_x_contact=[0 0 1 2 3 4 0 0]

afterwards I'm creating a function, that uses the corresponding value of the vector within.

For example:

function Integral = pressure_integral(x)
Integral = g_x_contact(x).*(x/2)    
end

So I want the function to use the value at position x and calculate the according steps afterwards.

Here the promt-line >> pressure_integral(6) should calculated with the sixth element: 4.*(6/2)=12

Instead I get the error-Message

Unrecognized function or variable 'g_x_contact'.

Error in pressure_integral (line 6)
Integral = g_x_contact(x).*(x/2)

Can anybody give me a hint, how the access the Vector?

Thank you in advance and very best

Christian

Answer 1

[Bob Thompson]

I believe this is the purpose of global variables, but I could be wrong. I don't really use them much.

[Stephen23]

Much better than global variables (which should be avoided):

• nested functions
• passing data as input argument (recommended by the MATLAB documentation).

[Christian S.]

Thank you for your answers Bob and Stephen,

I came across the method of passing data as an input. I thought my targeted use for this fuction -to calculate an integral- will be problematic, if I give the function two input arguments.

My detailed explenation:

The p(Xi) is my precalculated Vector with different values.

Is it expedient to do this with the method of passing data?

Very best

Christian

[Bob Thompson]

Stephen, good to know. So glad they taught me good code practices in school.

Christian, why don't you just pass in the extra variable?

function Integral = pressure_integral(x,g_x_contact)
Integral = g_x_contact(x).*(x/2)    
end

[Stephen23]

"I thought my targeted use for this fuction -to calculate an integral- will be problematic, if I give the function two input arguments."

It isn't problematic at all. This explains what you need:

https://www.mathworks.com/help/matlab/math/parameterizing-functions.html

[Christian S.]

Thank you guys very much!