Graphing a function with multiple symbolic variables as a 3D surface

Hi there,

I have a function that consists of 2 symbolic variables and a constant. I am trying to graph the function as a 3d surface between set boundaries.

I am attempting to graph

Y=-(((c^2)-r^2)/(r*2))*dz

Where r is a symbolic variable and dz is a function of the symbolic variable z. c is a constant.

I need my r values to be between 0 and 25 and z to be between 0 and 105.

I tried using ‘subs’

Z=linspace(0,105,6)
R=linspace(0,25,6)
Y2=subs(Y,[r,z],[R,Z])

However, this leads to an error.

So, I am having trouble figuring out how to introduce these boundaries to the symbolic variables in order to graph the function.

Would love to know if there is a way to do this?

Thanks so much!

Answer 1

[Walter Roberson]

Y2 = subs(Y,{r,z},{R,Z.'})

[Walter Roberson]

but if this is just plotting then fsurf()

[Navya Jay]

Thanks Walter!

I think the fsurf() function is what I'm looking for!

However, I tried the fsurf() function and it came up with an issue with the matrix size.

Y2=@(r,z)-(((c(x)^2)-r^2)/(r*2))*dz
fsurf(Y2,[0 25 0 105])

"The following error was reported evaluating the function in FunctionLine update: Incorrect dimensions

for raising a matrix to a power. Check that the matrix is square and the power is a scalar. To perform

elementwise matrix powers, use '.^'."

[Walter Roberson]

Y2=@(r,z)-(((c(x).^2)-r.^2)./(r*2)).*dz
fsurf(Y2,[0 25 0 105])

[Walter Roberson]

but you said that c is a constant and now it is a function of x??

[Walter Roberson]

And you do not use z in the formula, but you use x that is not defined?

[Navya Jay]

So sorry! I simplified the formula as I wrote it here but forgot to write the c(x) as c. c(x) is from a reference to a spreadsheet, but in the formula its a constant (specifically 27.5). dz is a function of z.

[Navya Jay]

Thank you so much for your help! I used

Y2=@(r,z)-(((c(x).^2)-r.^2)./(r*2)).*dz

and I no longer get that error!