SOLVE command with SYMS

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Eric Hong
Eric Hong 2012-9-6
Hi,
I have the Symbolic Math Toolbox. However, I can't even perform the following operation, which is copied and pasted from the Mathworks website on the usage of Symbolic Math Toolbx.
syms x
solve(x^2 + 4*x + 1 == 0)
The error says the following:
??? Input argument "x0" is undefined.
Error in ==> solve at 56
x=x0;
This isn't really what I'm trying to do. I have a system of non-linear equations and I get a whole different error messages, but the fact that I can't even perform a simple solving operation such as the above makes me think that there's something fundamentally wrong.
Can you please help me?
Thanks,
Eric
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Eric Hong
Eric Hong 2012-9-6
编辑：Eric Hong 2012-9-6
Yes, I think it is the version issue. I have 7.12.0 (R2011a).
I did have a script with the same name 'solve. m'
I removed it from the path and now it says:
>> which -all solve C:\Program Files\MATLAB\R2011a\toolbox\symbolic\symbolic\solve.m
Now I have a different error message:
??? Error using ==> char
Conversion to char from logical is not possible.
Error in ==> solve>getEqns at 189
vc = char(v);
Error in ==> solve at 67
[eqns,vars] = getEqns(varargin{:});
But now the same operation without the logical equal sign now works.
Thanks,
Eric
Walter Roberson
Walter Roberson 2012-9-6
Using the == in that context was not yet allowed in R2011a.

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采纳的回答

Azzi Abdelmalek
Azzi Abdelmalek 2012-9-6
编辑：Azzi Abdelmalek 2012-9-6
syms x
solve(x^2 + 4*x + 1)
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Azzi Abdelmalek
Azzi Abdelmalek 2012-9-6
to solve x^2 + 4*x + 1=5*x+1
solve(x^2 + 4*x + 1-(5*x+1))
Azzi Abdelmalek
Azzi Abdelmalek 2012-9-6
编辑：Azzi Abdelmalek 2012-9-6
or you don't need to use syms variables
solve('x^2 + 4*x + 1=0')

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