How to plot vector valued function with single input.

I wonder if this is even possible and the question itself is redundant. Normaly a vector valued function is plotted with 2 inputs:

[x,y] = meshgrid(-1:0.1:1);
fx = x.^2;
fy = 3.*y;
quiver(x,y,fx,fy)

in order that each (x,y) input in the coordinate plane is adressed to an output (I suppose). Probably that's rather a question for Mathstack, but while I'm at it: is it possible to plot a function that goes like f(phi) = [cos(phi); sin(phi)] ?

Answer 1

[Walter Roberson]

syms phi real
f(phi) = [cos(phi); sin(phi)];
fplot(f)

[Niklas Kurz]

Ah, somewhat selfexplaining.

[Niklas Kurz]

But can't you plot it like f(phi,0) = [cos(phi); sin(phi)]. How to achieve this?

[Walter Roberson]

You cannot do that.

If f in that syntax were a numeric array or a cell array, then the 0 would be an invalid index.

If f in that syntax is a symbolic function name that you are defining, then the arguments to f() on the left side of a symbolic function definition must each be scalar symbolic variable names or row vectors of symbolic variable names (unless there is only a single parameter, in which case it is permitted to be a column vector of symbolic variable names.) 0 is not a valid symbolic variable name, so f(phi,0) cannot be defined.

It is not possible to define a symbolic function in parts. For example it is not possible to define

f(0,0) = -1
f(0,phi) = sin(phi)
f(theta,0) = theta^2

Each symbolic function can only be defined in a single statement -- though the statement can use piecewise():

f(theta,phi) = piecewise(theta==0 & phi == 0, -1, theta == 0, sin(phi), phi == 0, theta^2, etc)