Declaring a global variable to be used across functions and/or scripts in MATLAB

Hi

I've declared a global variables I in a script file named "xyz.m"

global I;
T_P = ones(1,I);

which will call the following function:

[C_Prob] = Calculate_C_Prob();

The function, which is in another file named Calculate_C_Prob.m is defined as:

function [C_Prob] = Calculate_C_Prob();
 I = 5;
 for i=1:I
      t = prod(1-T_P(i+1:end));
 end

Now, I is a constant and should remain I = 5 in both the script as well as in the function.

Is the above declaration of the global variable correct? Also, T_P (whose value can change with time) be accessible in the function file? If not, then how to make it so?

Answer 1

[Walter Roberson]

global variables need to be declared in every function that they are used.

T_P will not be available to the function when you use that code. You could declare it global as well

[Syed]

How should i do that? Any example?

[Walter Roberson]

global T_P

exactly like your "global I"

[Image Analyst]

Or you could pass T_P in via the input argument list, if you change the declaration of Calculate_C_Prob() so that it's able to take input arguments.

[Syed]

By modifying:

function [C_Prob] = Calculate_C_Prob(T_P);
I = 5;
for i=1:I
   t = prod(1-T_P(i+1:end));
end

but when i run the function in the command line i get an error. Why is this so?

[Jan]

Please post the complete error message. When a function is defined with an input argument, you have to provide one.

[Syed]

here's the error that i get: Undefined function or variable 'T_P'.

[Jan]

@Syed: It is not useful to extract a tiny part of the error message, because important details are included in the complete message.

[Image Analyst]

You need to pass in T_P when you call it from the command line. For example

result = Calculate_C_Prob(42)