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Groups > comp.soft-sys.math.maple > #354

strange behavior in a while loop

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Hi,

I have the following code for a fixed point iteration in two dimensions:

Restart; with(linalg);
Gt:=matrix(2,1,[2-2*x2,1/2*sqrt((2-x1)*(2+x1))]);
#Maple command to get a vector as a function of x1 and x2;
G:=array@op@unapply([op](eval(Gt)),x1,x2):
# initial quantities
X0:=matrix(2,1,[0.5,0.5]);epsilon:=1e-12;Nor:=2;i:=1;
# loop
while Nor > epsilon do
    X1:=G(X0[1,1],X0[2,1]);
    Y:=evalm(X1-X0); 
    N:=evalm(transpose(Y)&*(Y));
    Nor:=evalf(sqrt(N[1,1]));
    X0:=X1;
    i:=i+1;
end do: 

If you run this, you'll see that from the second iteration, X0 and X1 are identical and I do not know why? It means that when X1:=G(X0[1,1],X0[2,1]); is performed (in loop 2) X0 gets the value of X1 right away and Y is then 0 and the procedure stops while it should not. I think there is some kind of a tricky thing happening inside Maple (13) but I am not sure what. I'd be happy to have your insight. Thanks

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strange behavior in a while loop pluton <plutonesque@gmail.com> - 2012-02-08 00:02 -0800
  Re: strange behavior in a while loop acer <maple@rogers.com> - 2012-02-08 00:37 -0800
    Re: strange behavior in a while loop pluton <plutonesque@gmail.com> - 2012-02-08 11:58 -0800

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