       Re: problem evaluating a function on a list

• To: mathgroup at smc.vnet.net
• Subject: [mg69888] Re: problem evaluating a function on a list
• From: dh <dh at metrohm.ch>
• Date: Tue, 26 Sep 2006 05:21:45 -0400 (EDT)
• References: <efacrp\$1vm\$1@smc.vnet.net>

```Hi Ruth,

f[..]:=If[condition,..,I]

if the condition is false, I is returned. If the condition is true,

things are a bit more complicated. You do some arithmetic with the

argument x. By chance you only use Listable operators. Therefore, if you

give a List as argument, your calculations return a List. On the other

hand, had you used e.g. a function that is not Listable, say f, the

result would not have been fully evaluated. In this case, you could use

e.g. Map.

Daniel

wtplasar at ehu.es wrote:

> Hi everyone,

>

>

> I have this function

>

> H[x_, om_,

>     or_, H0_] := If[Im[om - 4*om^(2/3)*or^(1/3) + 2*

>           or + 2*Sqrt[or]*Sqrt[om + or]] == 0. && -1 + om - 4*om^(2/3)

> *or^(1/

>             3) + 2*or + 2*Sqrt[or]*Sqrt[om + or] < 0, H0*((1 - om -

> 2*or - 2*

>       Sqrt[or]*Sqrt[om + or])*(1 + x)^2 + (Sqrt[or] + Sqrt[or + om*(1

> +

>           x)^3])^2),  I]

>

> and I want to evaluate it at a list

>

> xlist = {0.09, 0.17, 0.27, 0.4, 0.88, 1.3, 1.43, 1.53, 1.75};

>

> When I choose parameters so that a list of real values should be

> obtained everything seems to be fine as one can see if for instance we

> evaluate

>

> H[xlist, 0.4, 0.1, 70]

>

> (my result is {81.138, 92.4217, 108.473, 132.803, 261.891, 435.859,

> 503.238, 559.829, 699.774})

>

> whereas in the cases I would expect the result to be

> {I,I,I,I,I,I,I,I,I}

>

> I get simply one single

>

> I

>

> instead, as one can see from evaluation of

>

> H[xlist, -0.4, 0.1, 70].

>

> Can someone indicate why this happens, and how I can get the

> desired list which looks like {I,I,I,I,I,I,I,I,I}?

>

>

> Ruth

>

>

```

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