after command bottom, I want X=[d2;d4;d9]
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clc
clear
A=[2;4;9];
n=length(A);
for i=1:n
s = ['syms d' int2str(A(i))];
eval(s)
end
10 个评论
Geoff Hayes
2014-10-28
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
2014-10-28
Matt Tearle
2014-10-28
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
2014-10-28
Geoff Hayes
2014-10-28
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
2014-10-28
Geoff Hayes
2014-10-28
Why are you trying to create an array of symbols? How are you planning to use X?
Reza
2014-10-28
James Tursa
2014-10-28
@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
2014-10-29
@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.
回答（1 个）
James Tursa
2014-10-28
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
3 个评论
Reza
2014-10-28
James Tursa
2014-10-28
编辑：James Tursa
2014-10-28
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
2014-10-29
编辑：James Tursa
2014-10-29
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
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2014-10-29
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