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MathGroup Archive 1994

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Help to a beginner...

  • To: mathgroup at yoda.physics.unc.edu
  • Subject: Help to a beginner...
  • From: frazao at dsc.ufpb.br (Pos. COPIN Ronaldo Martins Nascimento Frazao (Prof. Bruno))
  • Date: Mon, 24 Jan 94 10:13:24 EDT

Dear Reader,

	I'm a beginner on the use of the "Mathematica" and I'm couldn't resolve the EDO system that follows (on Math notation).

m := {1, 1, 1, 0}

p := 0.5

r := { {0, 0, 0, 0}, {1, 0, 0, 0}, {1, 0, 0, 0}, {0, 1, 1, 0} }

d := { {0, 0, 0, 0}, {5, 0, 0, 0}, {4, 0, 0, 0}, {0, 3, 2, 0} }

int := {3, 5}

fq[ { i_, j_, t_ } ] := If[ t > d[[i]],
				Evaluate[ q[ j ][ t - d[[i]] ],
				Evaluate[ q[ j ][ t ]
				];

fm[ { i_, t_ } ] := If[ t >= int[[1]] && t =< int[[2]],
				m[[i]],
				0
				];
eq = Join[
		Table[ q'[i][t] == fm[ { i, t } ] +
				Sum[ r[[i, j]] * fq[ {i, j, t} ], {j, 1, 4} ],
			{i, 1, 4}
		     ],
		Table[ q[i][0] == 2, {i, 1, 4}
		     ]
	  ]

sol = NDSolve[ eq, Table[ q[i], {i, 1, 4} ], {t, 0, 10} ]

Plot[ Evaluate[ Table[ q[i][t], {i, 1, 4} ] /. sol ], {t, 0, 10} ]

	And it doesn't work...
	
	For your understanding:

	1. The function fm is equal to m in the interval int = {3,5} and is equal to zero outside this domaine.

	2. The function fm was defined to represent the function q[i][t] witch is equal to q[i][t] for t =< d[[i]] and is equal to q[i][ t - d[[i]] ] for 
t > d[[i]].

	The specification #1 has worked well, but when I introduced the function fq the NDSolve no more was capable to resolve the system.

	I suppose that the problem is that in the first case ( the use of fm) the substitution is done for a value that is an element of an array ( m[[i]] ), whereas on the second case the substitution is done for the specification of a function.

	How it can be resolved this kind of problem?

	I ask you, if possible, to reply this mail as soon as possible, because I depends onthe solution of this problem to conclude a paper that I'm my work on and I have a deadline to do this.

		My best regards,   

		Ronaldo Frazao 





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