matlab code for lagrange methode
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i getting this error :
Operator '-' is not supported for operands of type 'cell'.
Error in untitled (line 20)
code
clear all;
close all;
clc;
%%
syms x;
%Data
%Input data
n=input('Enter no. of node points:'); %no. of node points
%enter x values
a=input('Enter the values of x in braces:');
if length(a)==n
b=input('Enter the values of y in braces:');
%calculation of coeffiecients
for i=1:n
for j=1:n
c.c(i,j)=(a(1,i)-a(1,j));
end
end
c=c.c;
q=size(c);
c=c';
c(c==0)=[]; %deleting the zero values from the matrix
c=reshape(c,q(2)-1,q(1));
c=c';
j=1;
for i=1:n
d.d(i,j)=prod(c(i,:));
end
d=d.d;
d=d';
for i=1:n
coff.coff(i,j)=b(1,i)./d(1,i);
end
coff=coff.coff;
coff=coff'; %coefficients
%%
for i=1:n
for j=1:n
p.p(i,j)=(x-a(1,j));
end
end
p=p.p;
m=size(p);
p=p';
p(1:n+1:end)=[]; %deleting the diagonal elements
p=reshape(p,m(2)-1,m(1));
%%
p=prod(p);
pol=coff.*p;
pol=sum(pol); %Lagrange polynomial
%%
l=input('Enter a value to compute the b value:');
output=subs(pol,l);
%%
%Displaying output
disp('');
fprintf('Value of input x:=%f\n',double(output));
%%
if l>max(a)
x=min(a):0.1:l;
y=subs(pol,x);
plot(x,y,'r');
xlabel('X')
ylabel('Y')
else
x=min(a):0.1:max(a);
y=subs(pol,x);
plot(x,y,'r');
xlabel('X')
ylabel('Y')
end
else
display('Error: Values of x exceeds the number of node points')
end
%End of code
2 Comments
madhan ravi
on 7 Apr 2020
That’s why preallocation is really important. Preallocate variable before the loop to avoid ambiguities. You’re creating struct inside loops.
Answers (1)
Nagasai Bharat
on 25 Aug 2020
Hi Razan,
It is my understanding that you are performing some numerical computation using a cell array taken as input. To access an element of type cell array, curly brackets ‘{}’ to be used instead to parenthesis ‘()’. Or the cell array should be converted to matrices using cell2mat function.
Changes to your code as below should work.
if length(a)==n
b=input('Enter the values of y in braces:');
%calculation of coeffiecients
for i=1:n
for j=1:n
c.c(i,j)=(a{1,i}-a{1,j});
end
end
c=c.c;
q=size(c);
c=c';
c(c==0)=[]; %deleting the zero values from the matrix
c=reshape(c,q(2)-1,q(1));
c=c';
j=1;
for i=1:n
d.d(i,j)=prod(c(i,:));
end
d=d.d;
d=d';
for i=1:n
coff.coff(i,j)=b{1,i}./d(1,i);
end
coff=coff.coff;
coff=coff'; %coefficients
%%
for i=1:n
for j=1:n
p.p(i,j)=(x-a{1,j});
end
end
p=p.p;
m=size(p);
p=p';
p(1:n+1:end)=[]; %deleting the diagonal elements
p=reshape(p,m(2)-1,m(1));
%%
p=prod(p);
pol=coff.*p;
pol=sum(pol); %Lagrange polynomial
%%
l=input('Enter a value to compute the b value:');
output=subs(pol,l);
%%
%Displaying output
disp('');
fprintf('Value of input x:=%f\n',double(output));
%%
if l>max(cell2mat(a))
x=min(cell2mat(a)):0.1:l;
y=subs(pol,x);
plot(x,y,'r');
xlabel('X')
ylabel('Y')
else
x=min(cell2mat(a)):0.1:max(cell2mat(a));
y=subs(pol,x);
plot(x,y,'r');
xlabel('X')
ylabel('Y')
end
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