Lagrange Interpolation singleton error

Question

Mitul Dattani 2019-3-6

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/448688-lagrange-interpolation-singleton-error

回答： Vijaya Lakshmi Chagi 2019-3-13

Hi, I've been give code and have to add a line in to complete a Lagrange Interpolation, I googled it and found a couple threads tried them out but got the error saying:

Assignment has more non-singleton rhs dimensions than non-singleton subscripts
Error in cw1>my_interpolation (line 404)
				L_k(k,:)=L_k(k,:).*(x-x(j))/(x(k)-x(j));

The code causing the error is:

function P = my_interpolation(x,y,N)
	N_points = length(x); %the number of interpolation points from the input data
	X = linspace(min(x),max(x),N); % creates a uniform vector of points from min(x) to max(x) with resolution N of the interpolating polynomial (not to be confused by the number of data points)
	X=X'; % row vector to column vector
	P = zeros(N,1); % creates an empty vector of zeros for interpolating polynomial
	for k=1:N_points % loop over data points
		L_k = ones(N,1);  % defines initial Lagrange basis polynomial
	    for j=1:N_points % second loop over data points
	        if(k~=j)      % conditional statement
				
				%*************************** task 3 *************************************
				%  You need to complete the next line of code
				%  This line generates the Lagrange Basis Polynomials L_k used in the algorithm for the Lagrange Interpolating Polynomial
				L_k(k,:)=L_k(k,:).*(x-x(j))/(x(k)-x(j));	
					
				%***************************** end of task 3 ***********************************
	        end
	    end  
		P = P + y(k)*L_k;	
	end
end

The line in between the comments is the one ive added. Any help is much appreciated even a push in the right direction.

Thanks

Mitul

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Answer 1

Vijaya Lakshmi Chagi 2019-3-13

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/448688-lagrange-interpolation-singleton-error#answer_365162

在 MATLAB Online 中打开

Hi,

The error message occurs when you try to assign to a variable, but the indices of the left- and right-hand side of the assignment are incompatible. For example,

A(1) = [1 2 3];

throws this error because the size of the left-hand side is 1-by-1, but the size of the right-hand side is 1-by-3.

In your case, the RHS 'L_k(k,:).*(x-x(j))/(x(k)-x(j))' might be returning an array or vector which is not compatible with the LHS. Could you try storing the result of the RHS in a new varibale and check for its dimensions.