What's wrong this code in Matlab: numeric::solve(x^6 - PI*x^2 = sin(3), x)

Question

I'm new to Matlab and I'm attempting to use it to solve equations numerically. I consulted the Matlab documentation, found the following code:

numeric::solve(x^6 - PI*x^2 = sin(3), x)

I tried to execute it, but Matlab says:

numeric::solve(x^6 - PI*x^2 = sin(3), x)
         |
Error: Unexpected MATLAB operator.

I'm confused. Could you tell me what's wrong? I'm using Matlab R2013a on OS X Mavericks.

score 2 · Answer 1 · answered Mar 08 '14 at 08:59

2

try using

syms x
sol_x = solve(x^6 - pi*x^2 == sin(3), x);
sol_x = sym2poly(sol_x);

answered Mar 08 '14 at 08:59

Ankush

235
3
14

score 1 · Answer 2 · answered Mar 08 '14 at 09:34

1

You try to use a command that only works in the MuPAD Notebook Interface in MATLAB. The documentation got better over time pointing this out. Does 2013a include the vpasolve command? If yes, that is probably what you are looking for.

answered Mar 08 '14 at 09:34

Christopher Creutzig

8,656
35
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According to the [release notes](http://www.mathworks.com/help/symbolic/release-notes.html#bti4vnc-1), [`vpasolve`](http://www.mathworks.com/help/releases/R2012b/symbolic/vpasolve.html) was added in R2012b. – horchler Mar 08 '14 at 18:12

score 0 · Answer 3 · answered Mar 08 '14 at 18:10

Perhaps you typed "solve" and "matlab" into Google and came across this page. Note the warning in the yellow box at the top of the page that @ChristopherCreutzig alluded to in his answer. MuPAD is a separate environment available to Matlab users – type mupad in your command window and you'll be able to run your command – but its functions are not directly callable from within Matlab. Many (if not most) of the functions in the Symbolic Math toolbox use the MuPAD engine under the hood. In your case you can call numeric::solve from within Matlab like this:

syms x;
s = feval(symengine, 'numeric::solve', x^6 - sym(pi)*x^2 == sin(3), x)

or using the older string format:

s = feval(symengine, 'numeric::solve', 'x^6 - pi*x^2 = sin(3)', 'x')

The output of either can then be converted to double precision column vector with s = double(s.'). However, in this case there seems to be no reason not to use sym/solve instead:

syms x
s = double(solve(x^6 - sym(pi)*x^2 == sin(3), x).');

See this for further details and other options for calling MuPAD functions from within Matlab.

What's wrong this code in Matlab: numeric::solve(x^6 - PI*x^2 = sin(3), x)

3 Answers3