plot x=f(y)

If I have a function given as x =f(y), how can I plot x as independent variable (x axsis) and y dependent variable (y axsis). I also need to control the range of both x and y.

x=y/(0.5+cos3y)

[Walter Roberson]

Could you confirm that you need to do this inside a mex routine? Or are you trying to use MATLAB Coder? I am trying to figure out what the Product tag you used implies for this.

Answer 1

[Walter Roberson]

In MATLAB, cos3y would be written as cos(3*y)

In MATLAB, if y is a vector, instead of using / you should use ./ -- so y./something instead of y/something

You have an implicit plot, so you should have a look at fimplicit()

[Mariam]

Let me rephrase my question, I am trying to make a code by matlab for plotting the following equation:

y= (0.5+cos(3*y))*x for both x and y to have the values: form 0 to 1e4. I have never come across with such an equation and I need to know how to solve it numerically.

All the best

[Walter Roberson]

In MATLAB, most of the time you need to express multiplication using the .* operator instead of the * operator.

You have an implicit plot, so you should have a look at fimplicit()

Hint:

If A(x,y) = B(x,y) then A(x,y)-B(x,y) = 0 must be true, and expression being 0 is what fimplicit() draws.

[Mariam]

I have tried the following:

f=@(x,y) y-(0.5+cos(3.*y)).*x;

fimplicit(f, [0 1e4 0 1e4])

an error message tells me that "undefined function or method 'fimplicit' for input arguments of type 'fuction handle'".

[Walter Roberson]

Which MATLAB release are you using? fimplicit() was added in R2016b.

[Mariam]

it is R2009a.

[Walter Roberson]

In R2009a, you can use

ezplot(f, [0 1e4 0 1e4])

[Mariam]

Many thanks.