How to input y' = 2x^3 - 2xy into matlab?

I input it as :

   2*x.^3-2*x*y;

but it didn't work.

I also tried this:

   (2*x.^3)-(2*x*y);

How can i fix this?

[James Tursa]

Didn't work in what way? What are the sizes of x and y? In the future, please give us some context for what you are doing, and also include the actual code you are using along with an exact copy&paste of the error message you are getting.

[S.R.]

Trying to plot a direction field.

Answer 1

[Walter Roberson]

syms y(x)
sol = dsolve( diff(y,x) == 2*x.^3-2*x*y )

The output will look something like

C4*exp(-x^2) + x^2 - 1

The C4 might be a different C* name. The C* name refers to a constant whose value depends upon the unspecified boundary conditions.

[Walter Roberson]

Try

     2*x.^3 - 2*x.*y

if your x and y are both vectors of equal length, or are both 2D arrays that are the same size.

If you are trying to do a 2D plot, then something like

xrange = linspace(-5, 7, 50);   %for example
yrange = linspace(pi, 8, 75);   %for example
[X, Y] = ndgrid(xrange, yrange);
u = 2*X.^3 - 2*X.*Y;
v = 0 * u;
quiver(X, Y, u, v)

Answer 2

[James Tursa]

Maybe this?

(2*x.^3)-(2*x.*y)

But hard to say if this is correct for you application since we don't know the sizes of x and y and how you are using this.

Answer 3

[Muhammad syafikh Mohd umar]

How to answer 3^2x.sqrt(9)=729