Finding error like unrecognized function or variable ' tridiagonal'

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Program:
% solution of 2D elliptical solution
% using Line Over Relaxation Method(LSOR)
% ep is accepted error%Tridiag: Tridiagonal equation zsolver banded system
clc;
clear all;
eps = 0.001;
omega = input(' enter the omega value: ');
beta = input (' enter the beta value: ');
n= 10000;
nx = 21;
ny = 42;
T(1:nx, 1:ny-1) = 0;
TN(1:nx, 1:ny-1) = 0;
T(1:nx, ny)= 100;
TN(1:nx, ny) = 100;
% its number of iteration
coeff = ( 2*(1+beta^2));
for iterations = 1:n
for j = 2:ny-1
a(1:nx-2) = -coeff;
b(1:nx-3)= omega;
c(1:nx-3)= omega;
for i = 2:nx-1
r(i-1) = - coeff*(1-omega)*T(i,j)-omega*beta^2*T(i,j+1)-omega*beta^2*TN(i,j-1);
end
r(1)= r(1)-omega*TN(1,j);
r(nx-2)= r(nx-2)-omega*TN(nx,j);
y = tridiagonal(c,a,b,r);
for k = 1:nx-2
TN(k+1,j)= y(k);
end
end
error = abs(TN-T);
totalerror = sum(error,'all');
if totalerror <= eps
break
end
T=TN;
end
iterations;
contour(TN');
RESULTS;
enter the omega value: 1.3
enter the beta value: 1
Unrecognized function or variable 'tridiagonal'.
Error in LSOR (line 28)
y = tridiagonal(c,a,b,r);
  4 Comments
Chetan Bhavsar
Chetan Bhavsar on 2 Oct 2021
Plus i have changed a part of code please check if its as per requirement or not
% b(1:nx-3)= omega;
% c(1:nx-3)= omega;
b(1:nx-2)= omega;
c(1:nx-2)= omega;

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Accepted Answer

Chetan Bhavsar
Chetan Bhavsar on 2 Oct 2021
Edited: Chetan Bhavsar on 2 Oct 2021
function main
% solution of 2D elliptical solution
% using Line Over Relaxation Method(LSOR)
% ep is accepted error%Tridiag: Tridiagonal equation zsolver banded system
clc;
clear all;
eps = 0.001;
omega = input(' enter the omega value: ');
beta = input (' enter the beta value: ');
n= 10000;
nx = 21;
ny = 42;
T(1:nx, 1:ny-1) = 0;
TN(1:nx, 1:ny-1) = 0;
T(1:nx, ny)= 100;
TN(1:nx, ny) = 100;
% its number of iteration
coeff = ( 2*(1+beta^2));
for iterations = 1:n
for j = 2:ny-1
a(1:nx-2) = -coeff;
% b(1:nx-3)= omega;
% c(1:nx-3)= omega;
b(1:nx-2)= omega;
c(1:nx-2)= omega;
for i = 2:nx-1
r(i-1) = - coeff*(1-omega)*T(i,j)-omega*beta^2*T(i,j+1)-omega*beta^2*TN(i,j-1);
end
r(1)= r(1)-omega*TN(1,j);
r(nx-2)= r(nx-2)-omega*TN(nx,j);
y = Tridiagonal(c,a,b,r);
for k = 1:nx-2
TN(k+1,j)= y(k);
end
end
error = abs(TN-T);
totalerror = sum(error,'all');
if totalerror <= eps
break
end
T=TN;
end
iterations;
contour(TN');
end
function x = Tridiagonal(e,f,g,r)
% Tridiagonal: Tridiagonal equation solver banded system
% x = Tridiagonal(e,f,g,r): Tridiagonal system solver.
% input:
% e = subdiagonal vector
% f = diagonal vector
% g = superdiagonal vector
% r = right hand side vector
% output:
% x = solution vector
n=length(f);
% forward elimination
for k = 2:n
factor = e(k)/f(k-1);
f(k) = f(k) - factor*g(k-1);
r(k) = r(k) - factor*r(k-1);
end
% back substitution
x(n) = r(n)/f(n);
for k = n-1:-1:1
x(k) = (r(k)-g(k)*x(k+1))/f(k);
end
end
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