m-file function for solving high order polynomial equation

2014 12 1
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更新时间：2014 12 2
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I want to build for solving polynomial equation for high order (example x^202+x^102+x^52+100) and apply other problem.
I write m-file in this form.
function [eig] = solvepoly(chareq)
eq = 'chareq';
eig = solve(eq);
end
Then I use this function. The answer isn't correct.
>> [eig] = solvepoly(@(x) x^2+2*x+1)
eig =
0
But I use this command in command window. I get this answer.
>> eq = 'x^2+2*x+1'; >> eig = xolve(eq)
eig =
-1 -1
Help me please.

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Star Strider
Star Strider 2014-12-1

1 个投票

This is easier:
syms x
p = x^202+x^102+x^52+100;
r = roots(sym2poly(p));
The ‘r’ variable will have all 202 roots.

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Panitnart
Panitnart 2014-12-2
I follow your suggestion in this m-file
function [r] = solvepoly(chareq)
syms x;
p = chareq;
r = roots(sym2poly(p));
end
and try to command window
>> [r] = solvepoly(@(x) x^2+2*x+1)
Undefined function 'sym2poly' for input arguments of type 'function_handle'.
Error in solvepoly (line 5) r = roots(sym2poly(p));
Star Strider
Star Strider 2014-12-2
I didn’t use an anonymous function in my code.
Since you did, all you need to do is to cast it as a symbolic function (using the sym function) and my code works just as well.
Try this:
p = @(x) x^202+x^102+x^52+100;
ps = sym(p);
r = roots(sym2poly(ps));
Panitnart
Panitnart 2014-12-2
I try to follow your suggestion. It's work.
Thank you very much for advice.
Star Strider
Star Strider 2014-12-2
My pleasure!
The most sincere expression of thanks here on MATLAB Answers is to Accept the Answer that most closely solves your problem.

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