Re: Dynamic question

*To*: mathgroup at smc.vnet.net*Subject*: [mg125239] Re: Dynamic question*From*: "djmpark" <djmpark at comcast.net>*Date*: Thu, 1 Mar 2012 05:35:50 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <32121567.62941.1330519007647.JavaMail.root@m06>

It's easy to get confused on that and WRI is not completely specific as to where Dynamic should go. But the general rule is that Dynamic goes around the "output" and not around the "input" to the "output" . If calculations are to be done then do them all inside the Dynamic. So the following works: X=8; Dynamic[If[x >= 5, "a", "b"]] a The FullForm of your statement is: If[GreaterEqual[Dynamic[x] 5], "a", "b"] Mathematica doesn't know how to further evaluate that. It just substitutes the current dynamic value in the displayed result. Sometimes one is doing a calculation with a set of primary dynamic variables and a set of secondary dynamic variables that are calculated from the primary variables. In the following x is a primary dynamic variable controlled by a Slider. The secondary variables are y and z. These are calculated from x in the calcAll routine. DynamicModule[{x = 3, y, z, calcAll}, calcAll[xvar_] := (y = 2 xvar; z = xvar^2); calcAll[x]; Row[{Slider[Dynamic[x, (x = #; calcAll[x]) &], {0, 5, 0.01}], Spacer[10], Dynamic[ Row[{"x = ", NumberForm[x, {3, 2}], ",", Spacer[5], "x y z = ", x y z}]]}] ] The calcAll routine is invoked by the second argument in the Dynamic statement within the Slider. # represents the current setting of the Slider. Dynamic is then also wrapped around the entire output. All the variables (x, y, z) are continually updated by the Slider. It wouldn't even make any sense to wrap Dynamic around y or z individually because they're not even primary dynamic variables. But they are all updated and the product evaluated. David Park djmpark at comcast.net http://home.comcast.net/~djmpark/index.html From: dominik.hezel at googlemail.com [mailto:dominik.hezel at googlemail.com] Hello, I'm stuck in program, because (simplified to the guts) x = 8; If[Dynamic[x] >= 5, "a", "b"] doesn't work. Can anyone tell me why - or even better, offer me a solution how to do this? thanks a lot!