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Untitled - Cdm.unimo.it

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Examples 277<br />

Therefore, one obtains<br />

(12.3.8) lim<br />

⎡<br />

⎣<br />

j→+∞<br />

¯p(k,j) n<br />

¯q (k,j)<br />

n<br />

⎤<br />

⎦ =<br />

⎡<br />

⎣ ¯p(k) n<br />

¯q (k)<br />

n<br />

⎤<br />

⎦, 1 ≤ k ≤ m.<br />

The scheme considered here was suggested in delfour, fortin and payre(1981)<br />

for fin<strong>it</strong>e-difference approximations. It is second-order accurate, i.e., the error in the<br />

variable t decays as h 2 . In add<strong>it</strong>ion, <strong>it</strong> preserves certain physical quant<strong>it</strong>ies. For<br />

example, using formula (3.5.1) for w ≡ 1, we can prove the discrete counterpart of<br />

(12.3.2), i.e., that the sum n i=0 Θ(k) n (η (n)<br />

i ) ˜w (n)<br />

i<br />

does not change w<strong>it</strong>h k.<br />

Figure 12.3.1 - Evolution of an approximate solution of equation (12.3.1).

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