Collocation method: Difference between revisions

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Suppose that the [[ordinary differential equation]]
:<math> y'(t) = f(t,y(t)), \quad y(t_0)=y_0, </math>
is to be solved over the interval [''t''<sub>0</sub>,&nbsp;''t''<sub>0</sub>+''h'']. Denote the collocation points by 0 ≤ ''c''<sub>1</sub>,&nbsp;< ''c''<sub>2</sub>< &hellip;,&nbsp; < ''c''<sub>''n''</sub>. For simplicity, it is assumed that the collocation points are all different1.
 
The corresponding (polynomial) collocation method approximates the solution ''y'' by the polynomial ''p'' of degree ''n'' which satisfies the initial condition ''p''(''t''<sub>0</sub>)&nbsp;=&nbsp;''y''<sub>0</sub>, and the differential equation ''p''<nowiki>'</nowiki>(''t'')&nbsp;=&nbsp;''f''(''t'',''p''(''t'')) at all points ''t''&nbsp;=&nbsp;''t''<sub>0</sub>&nbsp;+&nbsp;''c''<sub>''k''</sub>''h'' where ''k''&nbsp;=&nbsp;1,&nbsp;&hellip;,&nbsp;''n''. This gives ''n''&nbsp;+&nbsp;1 conditions, which matches the ''n''&nbsp;+&nbsp;1 parameters needed to specify a polynomial of degree ''n''.
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\end{align}
</math>
The collocation method is now given (implicitly) by
:<math> y_1 = p(t_0 + h) = y_0 + \frac12h \Big (f(t_0+h, y_1) + f(t_0,y_0) \Big), \, </math>
where <math> y_1 = p(t_0+h) </math> is the approximate solution at <math> t = t_0+h </math>.