Thomas Algorithm: 

(To solve Tri-diagonal system of equations)

function x = thomasfunc(a,b,c,r)

%Here thomasfunc(a,b,c,r) makes use of Thomas algorithm to calculate the

%value of x for a tridiagonal system

%a denotes lower diagonal of matrix A [0 a2 a3 a4]

%b denotes main diagonal of A [b1 b2 b3 b4]

%c denotes upper diagonal of A [c1 c2 c3 0]

%r denotes right hand side vector b 

gamma(1)=c(1)/b(1);

rho(1)=r(1)/b(1);

n=size(a,2);

for i =2:n

gamma(i)=c(i)/(b(i)-a(i)*gamma(i-1));

rho(i)=(r(i)-a(i)*rho(i-1))/(b(i)-a(i)*gamma(i-1));

end

x(n)=rho(n);

for i = 1:n-1

x(n-i)=rho(n-i)-gamma(n-i)*x(n-i+1);

end

x=transpose(x);

end