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Re: strange error

  • To: mathgroup at smc.vnet.net
  • Subject: [mg122326] Re: strange error
  • From: David Bailey <dave at removedbailey.co.uk>
  • Date: Tue, 25 Oct 2011 06:17:43 -0400 (EDT)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <j7u562$t8q$1@smc.vnet.net>

On 22/10/2011 11:16, Klemen Dovrtel wrote:
> Hello everybody,
>
> I defined a simple function that is composed of three functions, each for different range of argument/variable. The function was composed using If[] conditions. The problem is that i can't FindRoot of this composed function. I get an error "the function value is not a list of numbers with dimensions {1}", which is not true. Any idea how can i solve this?
>
>
> Mathematica print screen:
>
> http://www.shrani.si/f/t/vo/3jLzgMiy/prtscr.jpg
>
> Best Regards
> Klemen

The problem is that your function 'evaluates' even when its argument is 
not a number (remember that Mathematica can do algebra as well as 
numerics). The following version will fix this:

Test[m_?NumericQ] := Module[{ret},
    If[m <= 100, ret = 2 m];
    If[100 <= m <= 200, ret = 200 + 1 (m - 100)];
    If[200 < m, ret = 300 + 0.5 (m - 200)];
    N[ret]
    ];

BTW, why not post a link to a notebook containing a problem, rather than 
an image, which requires typing back into a notebook?

David Bailey
http://www.dbaileyconsultancy.co.uk




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