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Topic: Constraint definition is not valid: WHY?
Replies: 1   Last Post: Jul 2, 2013 12:33 AM

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Bob Hanlon

Posts: 906
Registered: 10/29/11
Re: Constraint definition is not valid: WHY?
Posted: Jul 2, 2013 12:33 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

You wrote ReplaceAll incorrectly.

v1 = express ./ Par should be written v1 = express /. Par

Perhaps this is just a typo in your e-mail and not how you wrote your code
since this would give an error.

Functions use square brackets; for example,

V1 = f(e1, x) should be written V1 = f[e1, x]

In the statement

NMaximize[{objopt > 0, constr == 0}, {e1, e2, x}, Method -> NelderMead]

there is no expression to be maximized, just two constraints: an inequality
and an equation.

The error message indicates a problem with the constraint "expression" but
you have not

defined expression in the code snippets shown.

Bob Hanlon

On Mon, Jul 1, 2013 at 5:48 AM, <> wrote:

> I am tring to use Nmaximize in Mathematica This is How I proceeded:
> 1) define a list of parameters: Par = {a->1, b->3, etc};
> 2) define two functions: f1: v1=express./Par f2: v2=express./Par
> After this the expression are numerical except for the variables:
> V1=f(e1,x) and V2=f(e2,x)
> The objective function to be maximized is V1/(e1+e2) I defined the
> constraint as constr=V1-V2;
> then I used the Nmaximize:
> NMaximize[{objopt > 0, constr == 0}, {e1, e2, x}, Method -> NelderMead]
> I obtained the following error:
> NMaximize::bcons: "The following constraints are not valid: "expression".
> Constraints should be equalities, inequalities, or domain specifications
> involving the variables"
> I checked that only those variables are present in the constraint and
> objective function (other are numerical parameters) I do not understand why
> this error appears can someone help me?
> Thank you
> Alex

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