Try to use solve but getting "Error in MuPAD command: Index exceeds matrix dimensions"

Hello,

I get the following error message when I try to use solve using a system of equations and specifying the variables to be solved for:

Error in MuPAD command: Index exceeds matrix dimensions.

Essentially, I have 7 equations with 3 variables (a, lambda1 and lambda2) and one parameter (2). Below is my source code. I am using the Student version of MATLAB R2010a.

syms a s lambda1 lambda2;

S = solve('lambda1 - lambda2 + 1=0','a>=0', 's/2 - a >= 0', 'a*lambda1=0','lambda2*(s/2 - a)=0','lambda1>=0','lambda2>=0','a','lambda1','lambda2');

Please note that when I take away either the 'a', 'lambda1', or the 'lambda2' (i.e. so that I am just solving for 2 variables instead of 3), then the error message goes away. But when I try to solve for all 3 variables 'a', 'lambda1' and 'lambda2', then I get the error message.

Answer 1

[Walter Roberson]

This appears to be the same bug as https://www.mathworks.com/support/bugreports/677110 except no trig is involved.

Workaround:

Call the MuPAD symbolic engine directly. For example,

>> S = evalin(symengine,'solve([p1-y1,p2-y2,p3-sin(y3)],[y1,y2,y3])')

[Trevor Gates]

Thank-you, that worked beautifully! Below is how I was able to implement it in my code:

text = ['solve([',eq1,', ', eq3, ', ', eq4, ', ', eq3a, ', ', eq4a, ', ', eq6a, ', ', eq6b, '], [a])'];

[a_sol] = evalin(symengine,text);