MacFormat 1994 August/August CD.bin/Shareware/Education/numericalmethods Folder/chap_4/lagran.m

Text File | 1994-06-05 | 735 b | 23 lines | [MATF/MATL]

function [C,L] = lagran(X,Y)
% [C] = lagran(X,Y)
% [C,L] = lagran(X,Y)
% Construction of the collocation polynomial.
% The method is Lagrange interpolation.
% X is the list of abscissas, input.
% Y is the list of ordinates, input.
% W is the coefficient list for the polynomial, output.
% L is the matrix for the Lagrange coefficient polynomials, output.
n1 = length(X);
n  = n1-1;
L = zeros(n1,n1);
for k=1:n+1,          % Form the Lagrange coefficient polynomials
  V = 1;              % by using poly(r1) to create a polynomial
  for j=1:n+1,        % with a known root, and conv(P2,P1)
    if k ~= j,        % which is polynomial multiplication.
      V = conv(V,poly(X(j)))/(X(k)-X(j));
    end
  end
  L(k,:) = V;
end
C = Y*L;