Symbolically solving vectors simultaneously

Hello, I have been trying to solve a vector using the symbolic toolbox and am running into an error that says "Error using maplemex

Error, (in MTM:-solve) 0 variables do not match undefined outputs.", I am currently trying to solve for a variable in a matrix that is equal to zero, below is an example.

syms q0
moment=[5*q0+25 6*q0+45 5*q0+45]
[q0]=solve(moment==0)

This specific example is solving moment equilibrium for a monocoque structure.

Is there a way to solve the seperate q0 values so its a vector like [q0_1 q0_2 q0_3] using the symbolic toolbox?

Thanks!!!

Answer 1

[Star Strider]

One solve statement (such as in the original post) also fails in R2022a. One option to get all of the solutions is arrayfun that should be available (another is an explicit loop) —

syms q0 
moment = [5*q0+25 6*q0+45 5*q0+45];
q0 = arrayfun(@(x)solve(x), moment)

q0 = 

.

[Ramses Young]

Trying that, copy and pasting your code, I get the error

"Error using arrayfun

Unsupported ARRAYFUN input type: sym"

[Star Strider]

Unfortunately, I cannot test my code in R2018a.

Option 2 —

syms q0 
moment = [5*q0+25 6*q0+45 5*q0+45];
for k = 1:numel(moment)
    q0(k) = solve(moment(k));
end

q0

q0 = 

.

[Walter Roberson]

arrayfun() might not be able to work with Maple sym, so using a loop might be the best.

[Ramses Young]

I decided to completely uninstall maple and reinstall all the matlab toolboxes and these to have fixed all the maple stuff that was causing issues. Kinda annoying that Maple makes the matlab stuff not work correctly. But thank you all for the help!

[Star Strider]

As always, my pleasure! (And thanks to Walter for his observations.)

Answer 2

[Paul]

q0 = sym('q0_',[1 3])

q0 = 

moment=[5*q0(1)+25 6*q0(2)+45 5*q0(3)+45]

moment = 

solve(moment==0,q0)

ans = struct with fields:
    q0_1: -5
    q0_2: -15/2
    q0_3: -9

[Walter Roberson]

I do not recall whether the interface to maple supports using sym that way to create a vector. Maybe?

[Ramses Young]

This didnt work for me, It is giving me the same error I put in the post... is there a way to go around this??

Thanks!