Lagrange interpolation (dup)

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 = 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;
                }
                return y;
            };
        graph = board.createElement('curve', ['x', polynomial, 'x', -10, 10], {curveType:'graph'});