Сделать так, что бы если среди коэффициентов встречались нули, то строки матрицы менялись бы местами

program asds;
 
const
e = 0.000001;
 
var
a, a1: array[1..10, 1..10] of double;
b, b1: array[1..10] of double;
x: array[1..10] of double;
n, i, j, k: integer;
z, r, g: double;
 
begin
//clrscr;
Write('vvedite poriadock: ');
readln(n);
writeln('Vvedite koeficenti sistemi i svobodnie chleni');
for i := 1 to n do
begin
for j := 1 to n do
begin
Write('a[', i, ',', j, ']= ');
readln(a[i, j]);
a1[i, j] := a[i, j];
end;
Writeln('b[', i, ']= ');
readln(b[i]);
b1[i] := b[i];
end;
for k := 1 to n do
begin
for j := k + 1 to n do
begin
r := a[j, k] / a[k, k];
for i := k to n do
begin
a[j, i] := a[j, i] - r * a[k, i];
end;
b[j] := b[j] - r * b[k];
end;
end;
for i := 1 to n do
begin
for j := 1 to n do
Write(a[i, j]: 0: 2, ' ');
writeln;
end;
for k := n downto 1 do
begin
r := 0;
for j := k + 1 to n do
begin
r += a[k, j] * x[j];
end;
x[k] := (b[k] - r) / a[k, k];
end;
writeln('Korni sistemi:');
for i := 1 to n do
Write('x[', i, ']=', x[i]: 0: 2, ' ');
writeln;
writeln('Proverka v sootvetstvie c matrisei b:');
 
for i := 1 to n do
begin
r := 0;
for j := 1 to n do
r += a1[i, j] * x[j];
writeln(abs(r - b1[i]), ' ');
end;
readln;
end.