Constructs the Lagrange interpolating polynomial.
| xy | It is a matrix the first column of which contains the x values, the second contains the corresponding y values. It is expected to be sorted by x. |
| return value | Interpolating polynomial. |
In comparison, the function polynInterp() does not calculate the coefficients, and hence is probably more efficient for a single interpolation.
xy = [-1,4; 4,8; 42,-88; 444, 827];
xunit = 1J;
yunit = 1V;
p=polynLagrange(xy * [xunit,0;0,yunit])
xmin = min(xy[...;0]);
xmax = max(xy[...;0]);
eps = (xmax-xmin)/200;
xmin -= 2*eps;
xmax += 2*eps;
x = (xmin..eps..xmax)*xunit;
y = p.polynEval(#x);
[! xy[...;0]*xunit, p.polynEval(#(xy[...;0]*xunit))' !]
plot(x,y)