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Re: Try again to send my message: problems about "for"

  • To: mathgroup at smc.vnet.net
  • Subject: [mg96571] Re: Try again to send my message: problems about "for"
  • From: dh <dh at metrohm.com>
  • Date: Mon, 16 Feb 2009 16:38:03 -0500 (EST)
  • References: <gnbkaa$3cg$1@smc.vnet.net>


Hi Laura,

curly bracket are used to denote lists not bracketing, you must use 

"(..)" for bracketing. Therefore "{-2+C1}==1" is not an equation.

Then, the function DE is not defined.

Further, a compound statement uses ";" as delimiter, not ",".

There is no {..} needed inside the For loop:

Fot[ ..; ..; ... ,++i]

hope this helps, Daniel





laura parisi wrote:

> Dear Mathematica Users,

> the last message was unreadable  and so i send it again.

> 

> 

> I've realized a loop using Euler method:

> For[i = 1, i < 2,

> {S = (1/2)*(N1^2/DE[i - 1]) - (1/2)*DE[i - 1]*\[Epsilon]rif^2,

> a[i] = DSolve[Derivative[1][\[Rho]][t] - S == 0, \[Rho][t], t],

> \[Rho][t] = \[Rho][t] /. a[i],

> \[Rho][t] = \[Rho][t] /. C[1] -> C1,

> eq = \[Rho][t] /. t -> (t1[[i]] - 1),

> a = Solve[eq == \[Rho][i - 1], C1],

> \[Rho][i] = \[Rho][t] /. {C1 -> a, t -> t1[[i]]},

>         DE[i] = DE[i - 1]*\[Rho][i]}; i++];

> 

> in this expression, N1 is stated like a sinusoidal function:

> N1 = N0 + B*Sin[\[Omega]*t];

> 

> and T1 is a vector of time:

> t1 = Table[i, {i, 20}]

> 

> All the other parameters are allocated:

> B = 1;

> N0 = 2;

> \[Omega] = 1;

> A = 1;

> E0 = 1;

> \[Rho][0] = 1;

> \[Epsilon]rif = 1;

> 

> The loop give me this error:

> Solve::eqf:{-2+C1}==1 is not a well-formed equation. >>

> 

> with C1 constant of integration.

> 

> 

> What can I do for this loop in this case and in a case if i want to

> reapet the loop for i<100?

> Is better to use "DO"?

> 

> 

> Help me..It's important.

> 

> Thank you!

> 




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