plotting a symbolic array of functions

I have a symbolic array in the form of [f(theta,phi) g(theta,phi) 0] where theta and phi are symbolic variables. The indicies of the array represent (x,y,z) coordinates which vary as functions of phi and theta. I dont think i can use fplot or ezplot or similar functions to plot this, so I'm wondering what is the best approach? Im looking for something like a scatter plot.

Answer 1

[Star Strider]

Use the matlabFunction function to convert the symbolic functions into functions that can be used numerically. Then, if ‘theta’ and ‘phi’ are vectors, use ndgrid or meshgrid to create the matrices from them that are necessary to evaluate both of them together.

[Cyrus Ghorbani]

Thank you, i managed to get it to work using those tools! This is the resulting donut:

Is it totally necessary to do this numerically? this plot had 2500 sets of (x,y,z) data points and was pretty slow and i'm wondering if there is a way to keep it symbolic.

[Star Strider]

As always, my pleasure!

The Symbolic Math Toolbox is significantly slower than the numerical approach, since it’s best use is to do one-off derivations and such, not anything repeated. That’s the reason I suggested using matlabFunction and then doing the rest of the calculations numerically, preferably using vectorised code.

I don’t know how you coded the result you got. I suggested using ndgrid or meshgrid to create matrices from the vectors, then using those matrices as the function arguments. That would likely be reasonably fast. If you used loops, you can get about a 20% increase in speed by preallocating the result matrices. That involves creating the result matrices before the loop as matrices of zeros, and then just indexing into them in the loop.