How to ensure that dynamically create symbolically variables are real?

Hello,

I'm creating symbolic variables dynamically and I wanted to ensure that the symbolic variables are real.

I have the code

clear all
index = {'1'};
List = {'A','B','C'};
A=sym(strcat(List,index))

How can I modify this to make sure that the symbolic variables stored in A are real? I have tried changing to A=sym(strcat(List,index),'real'), but this doesn't work.

I'm looking to do something like

    syms A1 B1 C1 real
    A = [A1 B1 C1]

except I want to declare the variable names dynamically.

(I can't assume that List will contain alphabetically ordered letters. It is whatever list the user inputs.)

Thank you, Kevin

[Matt Tearle]

I'm assuming you know that dynamically created variable names make for hideous programming, right? ( Obligatory link )

But maybe you have a reason, involving users and symbolic stuff, so... answer below.

Answer 1

[Kevin Bachovchin]

clear all
index = {'1'};
List = {'A','B','C'};
A=sym(sym(strcat(List,index)),'real')

[Walter Roberson]

Now try again with variable names that are more than one character long.

[Kevin Bachovchin]

It seems to work fine even when the variables names in List are more than one character.

clear all
index = {'1'};
List = {'AR','BRR','C'};
A=sym(sym(strcat(List,index)),'real')

Answer 2

[Matt Tearle]

This, maybe?

names = strcat(List,index,{' '})
eval(['syms ',names{:},'real'])
eval(['A = [',names{:},']'])

Ergh. I shall now go take a shower...

[Kevin Bachovchin]

I'm looking to obtain a symbolic matrix A such as

clear all
index = {'1'};
List = {'A','B','C'};
A=sym(strcat(List,index))

Is there a way I can modify this to force A to a matrix of real syms? I don't understand why A=sym(strcat(List,index),'real') doesn't work.

[Matt Tearle]

I don't understand the objection. You said:

I'm looking to do something like

    syms A1 B1 C1 real
    A = [A1 B1 C1]

except I want to declare the variable names dynamically.

As far as I can see, that's exactly what my code does -- I get A1, B1, and C1 as real symbolic variables, then A is a 1x3 sym created from them.

Answer 3

[Walter Roberson]

A(1:length(List),1) = sym(0);
for K = 1 : length(List)
  A(K) = sym(List{K});
end
A = sym(A, 'real');

The behavior you are trying to use does not work because there is no functionality for sym() that even approximates it. You can pass a single string (horizontal char vector) or you can pass an existing symbolic array or you can pass a numeric array. No syntax for multiple strings. No syntax for multiple existing symbolic arrays.

[Kevin Bachovchin]

The following code works fine

clear all
index = {'1'};
List = {'A','B','C'};
A=sym(sym(strcat(List,index)),'real')