%sistema tri diagonal

function[x]=solve_tri(a,b)

n=length(b);

for k = 1:n

%pivotagem parcial

     [modpivot,q]=max(abs(a(k:k+1,k)));

     q=q+k-1;

	if(q~=k);

	auxq=a(q,k:n);

	a(q,k:n)=(k,k:n);

	a(k,k:n)=auxq;

	auxb=b(q);

	b(k)=auxb;

	end

%triangularizaçao

     i=k+1;

     mult=a(i,k)/a(k,k);

     a(i,k)=0.0;

     a(i,k+1:n)=a(i,k+1:n);

     b(i)=b(i)-mult*b(k);

end

x=zeros(n,1);

x(n)=b(n)/a(n,n);

for i=n-1:-1:1

     soma=(i,i+1:n)*x(i+1:n);

     x(i)=b(i)-soma/a(i,i);

end;

return;