Subscript indices must either be real positive integers or logicals.

Subscript indices must either be real positive integers or logicals.

Error in ==> Vinci_DLR at 175 alpha_amb = alpha(Nu_amb, la_amb, do, 1);

My alpha-calculation is a very simple function within my m-file and works without error in a single run. For iterative approach I nested it in a while-loop and I got the error above at second iteration. Why? I have similar other functions in this while loop where this problem does not occur.

Examples:

Ra = Raleigh(dT_amb, L, amb_type); % Raleighnr. for ambient convection

Nu_amb = Nusselt(0, Pr_amb, Ra, 0, 0, 2) % Nusselt number

Answer 1

[Adam]

I assume alpha is meant to be a function?

Are you also naming a variable alpha within the same workspace? If so then that variable will take precedence and the line you quote will be interpreted as trying to index into the variable rather than pass arguments to the function.

On a similar note, 'alpha' is actually also the name of a builtin Matlab function. It may not be one you require to use within your code, but it is good practice generally to avoid stamping on names of builtin functions unless you actually want to over-ride them.

You can type

which alpha

or

which alpha -all

to find out if a name already exists as function or as a variable too.

Answer 2

[yonatan gerufi]

your example is very hard to understand.

you should use debug to catch the error.

try this method:

try
 your code..
catch
 display('error')   - put break point here!
end

now, when it stops see the value of indices.

good luck!

[Martin]

Hi Yonatan, thanks for your help. These are the values of the error:

??? Attempted to access alpha(19897.4,0.105,0.1082,1); index must be a positive integer or logical.

But the first loop has similar values and works without error, same as above mentioned functions.

Answer 3

[Martin]

Hello Adam,

thanks a lot, I didn´t know that "alpha" is an already built-in function. After renaming my function the code worked perfectly :-).

Best regards,

Martin