Question

I’m a beginner in Mathematica programming. My code is not running as expected. I wonder if anyone could examine what goes wrong? Here is part of the code.

F[{k_, n_, x_}] =
Which[k == 0, f[a, b, x],
k == 1, g[a, b, n, x],
k == 2, h[c, d, n, x]]

G[x_] = F[{0, 0, x}]

While[Extract[G[x], 1] != 3, G[x_] = F[G[x]]]

The functions f, g and h are defined by Which as is F, and they are all vector-valued so that it makes sense to iterate F. What I want to achieve is: given initial value {0,0,x}, keep iterating F until the first component of F becomes 3. Is there anything, e.g. syntax, wrong in the above code?

Thanks!

Answer 1

As jVincent mentioned, I would use := instead of = while defining F.

I would also use the built in NestWhile instead of manually iterating.

NestWhile[F, {0, 0, x}, Function[e, Extract[e, 1] != 3]]

I can’t quite comment on how to correct the code as written because I’m not entirely sure how reassigning G in the While works.