Going from structure to matrix

So I'm trying to dynamically solve a matrix and have it so I can reuse it next loop however solve seems to return a structure that I can't dynamically cast back into a matrix.

The only code I've found to do it dynamically fails for reason "CELL2MAT does not support cell arrays containing cell arrays or objects."

%Matlab solver test
NumberOfMasses = 20;
lamda = sym('lamda',[NumberOfMasses NumberOfMasses]);
test = lamda * eye(NumberOfMasses,NumberOfMasses);
eqn = lamda * eye(NumberOfMasses,NumberOfMasses) == eye(NumberOfMasses,NumberOfMasses)*2;
ans = solve(eqn,lamda);
cell2mat(struct2cell(ans))%needs to be a matrix for next loop

Is there something I'm missing to Dynamically cast "ans" back to a matrix? (Preferably without writing code that dynamically builds strings and runs getfield() on the struct)

Answer 1

[madhan ravi]

Why not use struct2array() ? Note: Don’t Name a variable named ans .

[Dion Richardson]

Ahhh thanks, completely missed it. Only issue now is that I have to reshape it every time. Is there anything else I'm missing because this seems like a decent work around. (Just a lot of redundancy in larger code bases and it also fails if the matrix gets turned into a scalar during development)

reshape(struct2array(anz),[NumberOfMasses NumberOfMasses])

I just noticed the warning on ans after I posted hahaha

[madhan ravi]

I don’t see any alternatives at the moment, if you get the desired result using reshape() then why not use it, anyhow you’re willing to use it in a loop??

[Walter Roberson]

>> anz = solve(eqn,lamda);
>> anz

anz = 

  struct with fields:

      lamda1_1: [1×1 sym]
      lamda2_1: [1×1 sym]
      lamda3_1: [1×1 sym]
      lamda4_1: [1×1 sym]
      lamda5_1: [1×1 sym]
      lamda6_1: [1×1 sym]
      lamda7_1: [1×1 sym]
      lamda8_1: [1×1 sym]
      lamda9_1: [1×1 sym]
     lamda10_1: [1×1 sym]
     lamda11_1: [1×1 sym]
     lamda12_1: [1×1 sym]
     lamda13_1: [1×1 sym]
     lamda14_1: [1×1 sym]
     lamda15_1: [1×1 sym]
     lamda16_1: [1×1 sym]
     lamda17_1: [1×1 sym]
     lamda18_1: [1×1 sym]
     lamda19_1: [1×1 sym]
     lamda20_1: [1×1 sym]
      lamda1_2: [1×1 sym]

Look at the order of the fields: all of the _1 appear then all of the _2 and so on. Is that the order that you want the matrix to show up as?

I suggest that instead of converting to array, that you use:

      subs(lambda, anz)
      

[Dion Richardson]

I'm prototyping mathematical functions that I want to later run in C++. My issue is I'm not great at maths so I often make mistakes and change parts of my formula. This occasionally means that in some cases weird conditions come up. The loop time is about 20-30 seconds for some of my code (which is fine for prototyping).

Subs works perfectly! Thanks so much, never would've expected that to be the case.

[madhan ravi]

Thank you sir Walter!