sym matrices get converted to struct

Hi,

I am working with symbolic expressions. After each computation, i save the resulting symbolic expression as an element in the matrix. Then I save these matrices in a .mat format, and load them later for use in another program. When I load it, the sym matrix gets automatically converted to struct class, and am unable to use this.

The warning reads,' Error occurred while trying to call loadobj on a sym object: Reference to non-existent field 's'. Class 'sym' is an unknown object class or does not have a valid 'loadobj' method. Object 'Uz43s' of this class is converted to struct'.

Here Uz43s was originally a symbolic matrix

The symbolic toolbox is installed properly. I am using MATLAB R2016a (version 9.0.0.341360) with Symbolic toolbox 7.0. I have also tried using higher versions of Matlab - R2017a with Symbolic math toolbox 7.2, and still receive this warning.

Answer 1

[Nate]

Hi Vaibhav,

What functions are you using in order to save and load your symbolic expressions? I am attempting to replicate the issue, so more information about your code would be very helpful. This is my naive attempt:

x = sym('x');

class(x)

y = sym('y');

matrix = [x y]

save( 'test.mat', 'matrix');

clear;

load( 'test.mat' );

This did not produce any errors, and it appears to reload the symbols successfully. Please let me know if you have more information.

[Vaibhav Raghavan]

Hi Nate,

I save symbolic functions (in my case functions of two symbolic variables x and z) as each element in the symbolic matrix.

For example, one of the entries is

U1 = C(n,p).*X(x,kx(n).*Z(z,ky(p));

where kx and ky are vectors, and I specified n and p since I use a for loop.

I had initially copied the code through the hard drive on to another computer, which is when I got this error. However, if I run the code on the same computer and save the files, then I am able to load it.

Have another query, the laptop I had initially created the program in is from the US, however all the computers I have tried to load the symbolic files in are in the Netherlands. Can local settings be a problem?

[Nate]

Could you clarify the difference between copying the code through the hard drive vs running the code on the other computer? My understanding is that you are copying both the M file and the MAT file, and that the error only occurs when you move the MAT file from one computer to the other and then try to load it. Is that correct?

[Vaibhav Raghavan]

Yes, that is right. The error occurs when I run the files on any other computer.

Answer 2

[Steven Lord]

While the MATLAB session in which you created and saved the data has Symbolic Math Toolbox available, I suspect the MATLAB session in which you're trying to load the symbolic matrix does not have Symbolic Math Toolbox installed. Check with the ver function that this product is installed.

[Vaibhav Raghavan]

Yes, the MATLAB session when I am trying to load the files has the same version of the symbolic math toolbox, that the original session had!

[Walter Roberson]

Please show the output of

which -all sym

on the system that the load fails on.

[Vaibhav Raghavan]

C:\Program Files\MATLAB\R2016a\toolbox\symbolic\symbolic\@sym\sym.m % sym constructor