How can i use a symbol as a variable ?

Hi

I want to define a varibale alpha_ks as a symbol \alpha_ks but an error will be appeared.

function [a, x, ...]= MFC ()

a='\alpha_ks';

x=5;

end

[Jan]

The please tell us the complete error message. It is much easier to fix an error than to guess, what the error is.

The posted code runs fine (except for the "...")

[KSSV]

I don't think you can use symbol as a variable..What's the necessity too by the way?

[dbmn]

If you want to display nice formulas, you could do so in the new live scripts.

In the (text based) code it doesn't make sense.

Answer 1

[dpb]

From

help isvarname
  ... valid variable name is a character string of letters, digits and
  underscores, with ... the first character a letter, ...

While an (extended) character, '\alpha_ks' is not in the set of letters, digits, underscores. Ergo, it can't be a variable name by itself nor even as part of a longer name within which it occurs. "Sometimes we just can't have everything we want."

Another comment mentioned it having to do with text-based code which isn't really the issue; the restriction is that Matlab is based on the C/C++ coding language internally and these are the same rules for valid variable names in C. Nothing says TMW couldn't have expanded the allowable character set inside the Matlab interpreter, but would add another parsing overhead step as any variable name outside the naming rules would have to have another internal name generated for it that would follow the internal coding rules; potentially another real speed bottleneck when also would need to translate that back for display. Much easier to just follow the rules as they exist despite the lack of being able to write code that looks as much like the algebra of the underlying expression as might like. I suspect these kinds of restrictions will loosen significantly over time, but "not yet".

[Steven Lord]

The reason for the variable name rules are not that MATLAB is based on C or C++ internally. Suppose we allowed variable names to start with numbers and/or contain special characters (other than underscore, which doesn't have another meaning in MATLAB.) How would you interpret this?

x = 1+y;

Is that adding 1 to the variable whose name is y and assigning the result to the variable x? Or is it assigning the value of the variable named 1+y to the variable x? If the workspace contained both variables y and 1+y, how would you disambiguate?

Okay, so maybe special characters are a bad idea. But having variables start with a number isn't so bad, right?

z = 3i;

Is z real or complex? It depends on whether you have a variable named 3i in the workspace. Since you can't, that's unambiguously complex. Or how about:

w = 2e+4

Is w 20000 or is it the sum of 4 and the variable named 2e?

In the original question, a useful substitute for the TeX expression could be alpha_ks. It's close enough to the way you'd say that expression with the Greek characters and subscript to be easily understood a week, a month, or six months later.

[dpb]

I still think of it as those are same reasons the rules exist in C/C++ (as well as others); hence I think of it in those terms. So perhaps it isn't strictly owing to the underlying language itself but it's the same problem in the compiler they're solving.

Don't see anything fundamentally against increasing the scope of what the character set could be albeit again still need the proscription of starting with character that is a letter where 'letter' could also include at least subset of unicode characters.

It just has to be unique in that it doesn't have an interpretation otherwise; there's no reason the greek alphabet (say) in a character set that contains such couldn't just as well be included in the definition of "letter".

[Walter Roberson]

Back in 2017, most versions of MATLAB did not use UTF8 encoding for the file, and so only 8 bit codes that did not use the UTF control sequences could be reliably used... and even then only if there was no conflicting 8 bit code. For this purpose a conflicting code would be punctuation in one character set but letter-like in another character set: with 8 bit codes you would not be able to tell which is which. It does not matter if in one character set 0xC3 is 'Ă' but it is 'Ä' in a different character set: you could treat both as letters. It would matter if a character was Ϋ in one character set but … (ellipsis) in a different character set as those have different roles and … would probably be expected to act the same way as ... (three periods)