Solving a Cubic Equation

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Matthew
Matthew 2012-11-5
I am new to Matlab and I can't work out how to solve this cubic equation.
(Q/Qw)^3-(Q/Qw)-(1/F^3)=0.
I have Qw and F both as 1x108 matrices and I am trying to solve this equation for Q.
I would like to be able to see the answers in Q as numbers as to extract them so Q/Qw against f could be plotted.
Any help would be much appreciated.

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Nathaniel
Nathaniel 2012-11-5
The built-in function roots is what you're looking for.
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Matthew
Matthew 2012-11-6
I don't think I did that, this is what i did.
I have Qw and F both as 1x108 matrices.
roots((Q/Qw)^3-(Q/Qw)-(1/F^3)=0)
|
Error: The expression to the left of the equals sign is not a valid target for an
assignment.
Nathaniel
Nathaniel 2012-11-12
So hopefully by now, you have read the documentation and learned the proper syntax.
In the interest of not leaving this thread hanging, this is the syntax for your equation. If you have 108 of them, then you'll need to put it in a loop.
Q = roots([1/Qw 0 -1/Qw -1/F^3]);

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