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Animate cannot use functions

Posted 11 years ago
I'm trying to animate a function with parameters, and it seems animate cannot handle a function definition, only the function description. For example, this works:
Animate[Plot[4 x^2 + a x^3 + 5 x, {x, -5, 5}], {a, -1, 1}]
But this does not work:
p[z_] := 4 z^2 + a z^3 + 5 z;
Animate[Plot[p[x], {x, -5, 5}], {a, -1, 1}]
and just gives a blank plot with no graph. Is Animate unable to handle functions?
3 Replies
Posted 11 years ago
Making a an argument of the function fixed the problem in the Animate, appreciated. Had no idea there were "local" and "global" concepts in the function definitions.
If I understand correctly what you are trying to write, your first argument ot the Plot function is not calling your funciton p with any arguments.  Also your function p is not explicitly a function of a.

Is this what you actually mean? (note the semicolon and the first argument of Plot)
p[z_, a_] := 4 z^2 + a z^3 + 5 z;

Animate[Plot[p[x, a], {x, -5, 5}], {a, -1, 1}]
POSTED BY: David Reiss
Posted 11 years ago
Hi Bruce,

The "a" inside of Animate is a local variable, and it is not the same as the global "a" that appears in your function. You can pass the local "a" from the Animate into your function as a second argument.
p[z_, a_] := 4 z^2 + a z^3 + 5 z; Animate[
Plot[p[x, a], {x, -5, 5}], {a, -1, 1}]
POSTED BY: Michael Hale
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