matrix dimensions must agree

6 Ansichten (letzte 30 Tage)
Amanda McGovern
Amanda McGovern am 4 Nov. 2019
Kommentiert: Walter Roberson am 5 Nov. 2019
I am writing a lagrange interpolator function and when runnign the test code, my program fails for most tests and i get "matrix dimensions must agree" error. I am not sure where the error is. Can anybody tell? Also, is it appropriate for me to be using .* as opposed to just * operators? Thanks.
function p = lagrangeval(x,y,w)
%% lagrangeval evalutates the Lagrange interpolant for a set of knots (x,y)
%% Inputs: numbers x1,x2,..xn; values f(x1),f(x2)..f(xn)
%% Output: p - the value of the polynomial going through the n data points
function p = lagrangeval(x,y,w)
%% lagrangeval evalutates the Lagrange interpolant for a set of knots (x,y)
%% Inputs: numbers x1,x2,..xn; values f(x1),f(x2)..f(xn)
%% Output: p - the value of the polynomial going through the n data points
n=size(x,2);
k=size(w,2);
p=zeros(n,k);
for i=1:n
p(i,1)=y(i);
end
for l=1:k
for i=1:n-1
for j=1:i
p(i+1,j+1)=(((w(l)-x(i-j+1)).*p(i+1,j))-((w(l)-x(i+1)).*p(i,j)))./(x(i+1)-x(i-j+1));
end
end
end
  3 Kommentare
Amanda McGovern
Amanda McGovern am 4 Nov. 2019
x = 0:2*pi/5:2*pi; y = sin(x); w = [3 4]
x = 0:2*pi/8:2*pi; y = sin(x); w = [3 4 5];
Walter Roberson
Walter Roberson am 5 Nov. 2019
I do not encounter any error messages when I pass the above values to your function.

Melden Sie sich an, um zu kommentieren.

Antworten (1)

David Hill
David Hill am 4 Nov. 2019
Length of x and y must be equal since they are points. The following functions evaluations lagrange polynomial at each value of w (any length).
function p = lagrangeval(x,y,w)
a=length(x);
b=ones(1,a-1);
p=zeros(1,length(w));
for i=1:a
p=p+arrayfun(@(z)y(i)*(prod(z*b-x(x~=x(i)))/prod(x(i)*b-x(x~=x(i)))),w);
end
end

Kategorien

Mehr zu Polynomials finden Sie in Help Center und File Exchange

Produkte


Version

R2019a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by