行列の対角線の３項のみ「０」以外の方程式。
input n;
dim a(n,3),b(n),x(n),s(n),r(n);
for i:=1 to n;
for j:=i-1 to i+1;
if j<1 or j>n then l1;
input a(i,j-i+2);
label l1;
next j;
next i;
for i:=1 to n;
input b(i);
r(i):=0;
next i;
s(1):=0;
for i:=2 to n;
s(i):=b(i-1);
for j:=i-2 to i-1;
if j<1 or j>n then l2;
s(i):=s(i)-s(j)*a(i-1,j-i+3);
label l2;
next j;
s(i):=s(i)/a(i-1,3);
next i;
x(1):=1;
for i:=2 to n;
x(i):=b(i-1);
for j:=i-2 to i-1;
if j<1 or j>n then l3;
x(i):=x(i)-x(j)*a(i-1,j-i+3);
next j;
x(i):=x(i)/a(i-1,3);
r(i):=x(i)-s(i);
next i;
x1:=b(n)-a(n,1)*s(n-1)-a(n,2)*s(n);
x(1):=x1/(a(n,1)*r(n-1)+a(n,2)*r(n));
for i:=2 to n;
x(i):=x(1)*r(i)+s(i);
next i;
end;