How to plot the following function?

Question

Say I have a function

f(x,y,theta,xi) = x*y*c*theta*xi;

where c is a function of theta and xi and is predefined as

c:=theta*xi+theta^xi^2;

so f is effectively a function of x, y, theta, xi.

when I do the

Plot3D[f[x,y,0.5,0.5],{x,0,1},{y,0,1}]

Mathematica could not automatically calculate the value of c.

How do I plot a function of this sort?

That is, it contains a parameter which is a expression of the variables.

Thank you.

It's not clear how you defined f. How it is done will affect how it works. Probably, the global variable theta in the definition of c is not the same as the local parameter theta in the definition of f. — Michael E2, Commented Jan 30, 2016 at 18:44

Bob Hanlon · Accepted Answer · 2016-01-30 20:37:32Z

2

Make c an explicit function of theta and xi

c[theta_, xi_] = theta*xi + theta^xi^2;

f[x_, y_, theta_, xi_] = x*y*c[theta, xi]*theta*xi;

Plot3D[f[x, y, 0.5, 0.5],
 {x, 0, 1}, {y, 0, 1}]

answered Jan 30, 2016 at 20:37

Bob Hanlon

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$\begingroup$ Hi Bob, thanks for your code. But when I run it, it gives "Tag Times in (theta\ xi)[theta_,xi_] is Protected."I understand that it is because I am passing a function to another function. $\endgroup$
– LazyGamer
Commented Jan 30, 2016 at 20:50
$\begingroup$ Could you please share your thought on how to overcome this problem- tag times is protected" in general? thanks! $\endgroup$
– LazyGamer
Commented Jan 30, 2016 at 20:51
$\begingroup$ @LazyGamer - The code as posted works. Clear all of your definitions or start with a fresh kernel. $\endgroup$
– Bob Hanlon
Commented Jan 31, 2016 at 0:05

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