"Invalid second data argument" error while using "plot" function (Lagrange Interpolation)

I want to take the graph of x and y points with plot function, pointx is okay, but there is a error with pointy1, and i think because it is a function respect to x.

When i delete @(x), it says "x is a undefined function or variable."

Can you help me?

clc;
clear all;

pointx = [-2 -1 0 1 2];
pointy1 =@(x) (2 - atan(x));
x = linspace(-5,5);
n = size(pointx, 2);
L = ones(n, size(x,2));

for i=1:n
    for j=1:n
        if (i~=j)
            L(i,:).*(x-pointx(j))/(pointx(i)-pointx(j));
        end
    end
end
y = 0;

for i=1:n
    y = y + pointy1(i)*L(i,:);
end

y1 = y;
plot(pointx, pointy1, 'r', x, y1, 'c--o');
hold on;

Answer 1

[Tommy]

You are correct, it is complaining because pointy1 is a function handle. You can obtain the output of pointy1 when evaluated at the x values within pointx by calling pointy1(pointx):

clc;
clear all;

pointx = [-2 -1 0 1 2];
pointy1 =@(x) (2 - atan(x));
x = linspace(-5,5);
n = size(pointx, 2);
L = ones(n, size(x,2));

for i=1:n
    for j=1:n
        if (i~=j)
            L(i,:).*(x-pointx(j))/(pointx(i)-pointx(j));
        end
    end
end
y = 0;

for i=1:n
    y = y + pointy1(i)*L(i,:);
end

y1 = y;
plot(pointx, pointy1(pointx), 'r', x, y1, 'c--o');
hold on;

This works because your pointy1 function is vectorized.

[Yigit Apaydin]

thank you, it helped very much.

[Tommy]

Happy to help!