Sum the solution of solve function

2012 2 23
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Dear friends,
When solving a system of equations by using S=solve()
I got this kind of result
S =
z11: [1x1 sym]
z12: [1x1 sym]
z13: [1x1 sym]
z21: [1x1 sym]
z22: [1x1 sym]
z23: [1x1 sym]
z31: [1x1 sym]
z32: [1x1 sym]
z33: [1x1 sym]
I would like to find the sum of S.
However it cant be done with sum(S) because: Undefined function or method 'sum' for input arguments of type 'struct'
I can do that manually by first, displaying the solutions, S=[S.z11 S.z12 S.z13 S.z21 S.z22 S.z23 S.z31 S.z32 S.z33] after that, I can finally use sum(S) to get the sum of S.
However, I found this is not practical when I have a huge number of solutions in S.
Is there any other way to get the sum of S? Any help will be greatly appreciated.
Thank you very much.
Sincerely,
Leonardo

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 采纳的回答

Walter Roberson
Walter Roberson 2012-2-23

0 个投票

SC = struct2cell(S);
plus(SC{:})
or
sum(cell2mat(struct2cell(S)))

更多回答（2 个）

Leonardo
Leonardo 2012-2-23

0 个投票

Hi Walter, Thank you for reply.
I tried both of them,
- for this one, SC = struct2cell(S); plus(SC{:})
I got this message:
??? Error using ==> sym.plus Too many input arguments.
- for this one, sum(cell2mat(struct2cell(S)))
I got this message:
Cannot support cell arrays containing cell arrays or objects.
However, converting from structure to cell does work!
I tried this,
SC = struct2cell(S);
for i = 1:9 %9 is the number of solutions in this case
SCS(i) = SC{i};
end
sum(SCS)
and it is working now! Thank you very much for your help. Cant do this without you.
Sincerely,
Leonardo
Bjorn Gustavsson
Bjorn Gustavsson 2012-2-23

0 个投票

I can't get Walter's solution to work in my version of matlab (7.8.0.347 (R2009a)). There S is a sym object, and then this works:
S = solve('(x-x1)*(x-x2)*(x-x3)=0');
sum(S)
ans =
x1 + x2 + x3
What versions are you using?

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Leonardo
Leonardo 2012-2-23
Hi Bjorn,
Im using R2010a
Apparently in my case, sum is not working for input arguments of type 'struct'.
Therefore, I convert 'struct' to 'cell' as I wrote in my previous message.
Thank you for your reply ^^

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