Error using str2sym (line 83) Unable to convert string to symbolic expression: L 1 (C 103): BADCH: Invalid character(s).

Hi everyone, I am unsuccessful in converting string to symbolic expression on this code:

https://www.dropbox.com/s/xuauj97inby8o5m/IntegratedModelAnalytical.m?dl=0

What can I do?

Answer 1

[Star Strider]

You are using the Unicode ‘En Dash’ (decimal 8211, hex 2013) instead of a normal hyphen (decimal 45, hex 002D) for your minus and negation signs.

You also have a ‘hanging’ negative:

Eq1 = ('n + 2*d -((e*6.24*n)/(n^2 +6.24*n + 6.24*5.68e-5))- 2*((e*6.24*5.68e-5)/(n^2 + 6.24*n + 6.24*5.68e-5))–((h*1.7e-3*n)/(n^2 + 1.7e-3*n + 1.7e-3*6.55e-8))– 2*((h*1.7e-3*6.55e-8-)/(n^2 + 1.7e-3*n + 1.7e-3*6.55e-8))- 5.3e-8/n=0');
(SCROLL RIGHT) →                                                                                                                                                                     ↑ ← HERE

The correct version is:

Eq1 = 'n + 2*d - ((e*6.24*n)/(n^2 + 6.24*n + 6.24*5.68e-5)) - 2*((e*6.24*5.68e-5)/(n^2 + 6.24*n + 6.24*5.68e-5))-((h*1.7e-3*n)/(n^2 + 1.7e-3*n + 1.7e-3*6.55e-8)) - 2*((h*1.7e-3*6.55e-8)/(n^2 + 1.7e-3*n + 1.7e-3*6.55e-8)) - 5.3e-8/n=0';

There are other problems. I will let you solve them.

[Dursman Mchabe]

Thanks a lot for the comments, I will check all my minus and negative signs, and try to run the code again.

[Star Strider]

As always, my pleasure.

When I ran your code, there were no more minus-sign or other Unicode problems, only some missing-variable errors. That may simply be a mis-spelling.

It was actually easy to solve the ‘En Dash’ problem, though. I removed the single quotes from your ‘Eq1’ string, and the MATLAB Editor highlighted each ‘En Dash’ in red.

[Dursman Mchabe]

You made it easy for me as well. Thanks.

[Dursman Mchabe]

The error I'm dealing with now is

"Undefined function or variable 'dEq8_char'.

Error in IntegratedModelAnalytical (line 78) dEq6, dEq7,dEq8_char{:},dEq9_char{:},dEq10_char{:},...

>> "

There is probably something wrong with my definition of dEq8_Char as

"dEq8_Char =SymArray2CharCell(dEq8);"

In the example I am following, it was defined like that, and it worked. See attached or dropbox link

https://www.dropbox.com/s/4i5mgi5wvdva7ug/SolveExample.m?dl=0

I will try to find out.

[Star Strider]

As always, my pleasure.

If you are setting up differential-algebraic equations, the Symbolic Math Toolbox has several functions for them, and links to the appropriate numeric solvers. For an overview, see Solve DAEs Using Mass Matrix Solvers (link) and see odeFunction (link) for its documentation and links to several related functions.

The Symbolic Math Toolbox functions first appeared in R2015a.

[Dursman Mchabe]

I did DAEs method for about three months, see the attached files, it is some how more challenging. I tried both ODE15s and ODE15i. The errors were never ending.

[Star Strider]

I have no recent experience with DAEs.

It will be best if you open a new Question describing your current problem. There are others here much more knowledgeable with respect to DAEs in MATLAB than I am.

[Dursman Mchabe]

Actually, I have been doing that for some time now, DAEs are just challenging. See the links below:

https://www.mathworks.com/matlabcentral/answers/412270-this-dae-appears-to-be-of-index-greater-than-1?s_tid=mlc_ans_email_view#comment_600007

https://www.mathworks.com/matlabcentral/answers/414912-error-using-vertcat-dimensions-of-arrays-being-concatenated-are-not-consistent?s_tid=mlc_ans_email_view#answer_332830

I only had success with IVPs and BVPs. That is the reason I am also trying DSOLVE coupled with SOLVE. It will give me analytical solutions for all the variables.