Lagrange interpolation (dup): Difference between revisions
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A WASSERMANN (talk | contribs) No edit summary |
A WASSERMANN (talk | contribs) No edit summary |
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var polynomial = function(x) { | var polynomial = function(x) { | ||
var y = 0.0; | |||
for (var i=0;i<4;i++) { | |||
var t = p[i].Y(); | |||
for (var k=0;k<4;k++) { | |||
if (k!=i) { | |||
t *= (x-p[k].X())/(p[i].X()-p[k].X()); | |||
} | |||
} | |||
y += t; | |||
} | |||
/* | |||
var y = p[0].Y()*(x-p[1].X())*(x-p[2].X())*(x-p[3].X())/ | var y = p[0].Y()*(x-p[1].X())*(x-p[2].X())*(x-p[3].X())/ | ||
((p[0].X()-p[1].X())*(p[0].X()-p[2].X())*(p[0].X()-p[3].X()))+ | ((p[0].X()-p[1].X())*(p[0].X()-p[2].X())*(p[0].X()-p[3].X()))+ | ||
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p[3].Y()*(x-p[0].X())*(x-p[1].X())*(x-p[2].X())/ | p[3].Y()*(x-p[0].X())*(x-p[1].X())*(x-p[2].X())/ | ||
((p[3].X()-p[0].X())*(p[3].X()-p[1].X())*(p[3].X()-p[2].X())); | ((p[3].X()-p[0].X())*(p[3].X()-p[1].X())*(p[3].X()-p[2].X())); | ||
*/ | |||
return y; | return y; | ||
}; | }; | ||
Revision as of 17:14, 3 December 2008
Construct a polynomial of degree 3 through four given points.
board = JXG.JSXGraph.initBoard('box', {originX: 250, originY: 250, unitX: 50, unitY: 25});
// Axes
b1axisx = board.createElement('axis', [[0,0], [1,0]], {});
b1axisy = board.createElement('axis', [[0,0], [0,1]], {});
var p = [];
p[0] = board.createElement('point', [-1,2], {style:6});
p[1] = board.createElement('point', [0,-3], {style:6});
p[2] = board.createElement('point', [1,4], {style:6});
p[3] = board.createElement('point', [2,1], {style:6});
var polynomial = function(x) {
var y = p[0].Y()*(x-p[1].X())*(x-p[2].X())*(x-p[3].X())/
((p[0].X()-p[1].X())*(p[0].X()-p[2].X())*(p[0].X()-p[3].X()))+
p[1].Y()*(x-p[0].X())*(x-p[2].X())*(x-p[3].X())/
((p[1].X()-p[0].X())*(p[1].X()-p[2].X())*(p[1].X()-p[3].X()))+
p[2].Y()*(x-p[0].X())*(x-p[1].X())*(x-p[3].X())/
((p[2].X()-p[0].X())*(p[2].X()-p[1].X())*(p[2].X()-p[3].X()))+
p[3].Y()*(x-p[0].X())*(x-p[1].X())*(x-p[2].X())/
((p[3].X()-p[0].X())*(p[3].X()-p[1].X())*(p[3].X()-p[2].X()));
return y;
};
graph = board.createElement('curve', ['x', polynomial, 'x', -10, 10], {curveType:'graph'});
