after command bottom, I want X=[d2;d4;d9]

clc

clear

A=[2;4;9];

n=length(A);

for i=1:n

   s = ['syms d' int2str(A(i))];

   eval(s)

end

[Geoff Hayes]

tatina - please describe what you are attempting and what you would like to happen. It is not clear from your question or the source code provided. (For example, why are you using syms?)

[Reza]

Matrix X use for Solve Eq

[Matt Tearle]

What you've posted creates 3 symbolic variables, all 1-by-1. The command X = [d2;d4;d9] would work and create a 3-by-1 symbolic variable X. So you'll need to explain what the problem is. What do you want X to look like? Why is there a problem?

[Reza]

clc

clear

X=zeros(3,1)

A=[2;4;9];

n=length(A);

for i=1:n

   s = ['syms d' int2str(A(i))];

   eval(s)

X(i,1)=s

end

But;Error

[Geoff Hayes]

Tatina - try formatting your code to keep it distinct from the rest of your question and/or comments. Highlight the code portion and press the {} Code button.

And if you are observing an error, please provide the full error message (all that text which appears in red).

[Reza]

Subscripted assignment dimension mismatch

[Geoff Hayes]

Why are you trying to create an array of symbols? How are you planning to use X?

[Reza]

B matrix and C matrix is known , X Matrix is unknown , ===> B=C*X , X=?

[James Tursa]

@Geoff: Not sure of Tatina's reason, of course, but I have done this many times myself. E.g., to pass some symbolic matrices & vectors through a section of code to verify the resulting formulas match expected model. Etc.

[Geoff Hayes]

@James - thanks for the clarification. I've never used the Symbolic Toolbox so wasn't sure if you this was something that is expected/typical.

Answer 1

[James Tursa]

Is this what you want? Basically repeated your code, but get rid of the zeros initialization which will make X a double array (not what you want):

clc
clear
% X=zeros(3,1) % Commented out
A=[2;4;9];
n=length(A);
for i=1:n
   s = ['syms d' int2str(A(i))];   
   eval(s);
   X(i,1)=s; % Build up symbolic matrix
end

[Reza]

Error is Subscripted assignment dimension mismatch.

[James Tursa]

Sorry about that. I don't have MATLAB on the machine I am using right now, so can't verify the syntax. Try either X(i) = s, or pre-allocate X=[] and then use X=[X;s]. I know there is a way to do this because I have done it before. Could always build up a char array of the result and then eval it, I suppose.

[James Tursa]

Another attempt to get the symbolic vector defined in your code (still not on a machine w/MATLAB, so this is untested)

clc
clear
y='X=['; % Used to build up the symbolic vector string
A=[2;4;9];
n=length(A);
for i=1:n
   s = ['syms d' int2str(A(i))];   
   eval(s);
   y = [y 'd' int2str(A(i)) ';']; % Build up symbolic string
end
y(end) = ']'; % Replace the last ; with ]
eval(y); % Generate the symbolic vector