solving symbolic array to output a numerical solution

Hi there, I was wondering if I could get some feedback on a potential solution for this problem. I am trying to solve for ma3 and obtain a numerical value for each value used in the FLcD3 array. However, the output of Ma3 is a struct with fields. How do I get it so the solution is an array with the numerical values? I'm guessing I would need some form of a for loop but i'm not quite sure how to set it up.

PSW = 0.36:0.03:0.69; 
L12 = PSW*TL;
D = 0.03; 
Ma4 = 1;
P4 = 1.013;

Lc3 = TL-L12;
FLcD3 = 4*f*Lc3/D;

ma3 = sym('ma3', [1 length(PSW)]) ;
eqn1 = (-1./G).*(1-ma3.^-2)+((G+1)./(2.*G)).*log((((G+1)./2).*ma3.^2)./(1+((G-1)./2).*ma3.^2)) == FLcD3;
Ma3 = vpasolve(eqn1,ma3)

%This is the output I get

Ma3 = 
     ma31: [1×1 sym]
     ma32: [1×1 sym]
     ma33: [1×1 sym]
     ma34: [1×1 sym]
     ma35: [1×1 sym]
     ma36: [1×1 sym]
     ma37: [1×1 sym]
     ma38: [1×1 sym]
     ma39: [1×1 sym]
    ma310: [1×1 sym]
    ma311: [1×1 sym]
    ma312: [1×1 sym]

Answer 1

[madhan ravi]

struct2array(Ma3)

[Samuel Casallas]

I had previously tried that but I get the error:

Unrecognized function or variable 'struct2array'.

Is there a work around this?

[madhan ravi]

https://www.mathworks.com/matlabcentral/answers/493612-any-fixes-for-undefined-function-or-variable-struct2array#comment_821065

Answer 2

[VBBV]

From the reference link given by @madhan ravi, you can use struct2cell function and later convert the cell to double array using cell2mat function. And i think both struct2cell & cell2mat are documented well in Matlab

Ma3 = vpasolve(eqn1,ma3)
cell2mat(struct2cell(Ma3))

[Paulo Providencia]

Your suggestion did not work for me.

I have

struct2array(something)

in a program that used to run ok but today I got the message

Unrecognized function or variable 'struct2array'.

So I tried the suggestion of VBBV, and replaced by

cell2mat(struct2cell(something))

Unfortunatelly I got a new error:

CELL2MAT does not support cell arrays containing cell arrays or objects.

That´s terrible bad news for me. I cant understand the idea of MatLab of removing existing functions.

[Walter Roberson]

@Paulo Providencia

What shows up for

which -all struct2cell

built-in (/MATLAB/toolbox/matlab/datatypes/struct/@struct/struct2cell)   % struct method
/MATLAB/toolbox/parallel/array/distributed/@codistributed/struct2cell.m  % codistributed method

It is defined as a method of class struct so it would not be found if your something is not a struct

[Paulo Providencia]

Thank you very much for your SO QUICK answer!

Now that I read my previous message, I note that it is rather incomplete.

In fact, auxMLStructure is a struct (struct with fields: KNL22: [16×16 sym], with KNL22.mat created by another script). I first create auxMLStructure by loading KNL22.mat and thats when I try to manupulate it that I run into problem:

>> auxMLStructure = load('KNL22.mat');

>> matkElemNL22 = vpa(subs(cell2mat(struct2cell(auxMLStructure))))

Error using cell2mat (line 52)

CELL2MAT does not support cell arrays containing cell arrays or objects.

----

So, in fact , the problem is not with struct2cell but with cell2mat

[Torsten]

Why don't you directly apply

matkElemNL22 = vpa(subs(auxMLStructure.KNL22))

?

[Walter Roberson]

Side note:

As of R2025a (currently in pre-release), cell2mat() does support sym objects.