Solving a Cubic Equation

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.

Answer 1

[Nathaniel]

The built-in function roots is what you're looking for.

[Matthew]

Thanks for your answer but I still seem to be experiencing difficulties. I keep gettin this error

Error: The expression to the left of the equals sign is not a valid target for an assignment.

I have Qw and F both as 1x108 matrices. Is the problem in here? Can this be fixed?

Thanks

[Matt J]

It means the expression on the LHS of the line that gave you the error is a non-variable or something, for example:

 >> 1=x
   1=x
   |
  Error: The expression to the left of the equals sign is not a valid target for an
  assignment.

I'm sort of wondering if you've issued a command like

 (Q/Qw)=roots(...)

[Matthew]

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]

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]);