Sum the solution of solve function

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

Answer 1

[Walter Roberson]

SC = struct2cell(S);
plus(SC{:})

or

sum(cell2mat(struct2cell(S)))

Answer 2

[Leonardo]

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

Answer 3

[Bjorn Gustavsson]

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?

[Leonardo]

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 ^^