Реализация точности вычислений обратной матрицы

uses crt;
const nmax = 20;
type
matr = array[1..nmax,1..nmax] of real;
function Det(size:integer; var m : matr):real;forward;
function AlgDop(size:integer;m:matr;row,col:integer):real;
var temp : matr;
    i,j:integer;
    begin
for i:=1 to row-1 do
 begin
  for j:=1 to col-1 do temp[i,j]:=m[i,j];
  for j:=col+1 to size do temp[i,j-1]:=m[i,j];
end;
for i:=row+1 to size do
 begin
  for j:=1 to col-1 do temp[i-1,j]:=m[i,j];
  for j:=col+1 to size do temp[i-1,j-1]:=m[i,j];
end;
if (row+col) mod 2 = 0 then AlgDop := det(size-1,temp)
else AlgDop := -det(size-1,temp);
end;
 
function Det(size:integer; var m : matr):real;
var i:integer;
    r:real;
begin
if size = 1 then Det:=m[1,1]
else
if size = 2 then Det:=(m[1,1]*m[2,2]-m[1,2]*m[2,1])
else
 begin
  r:=0;
  for i:=1 to size do begin
    r := r + m[1,i]*AlgDop(size,m,1,i);
  end;
  Det:=r;
end;
end;
procedure ObrMatr(a:matr;var am:matr;n:integer);
var i,j:integer;
    dt:real;
begin
dt:=det(n,a);
if abs(dt)<1e-15 then begin
  writeln('Malenkiy opredelitel!');
  exit;
end;
for i:=1 to n do begin
  for j:=1 to n do am[i,j]:=AlgDop(n,a,j,i)/dt;
end;
end;
 
procedure print_matr(n:integer;var a:matr);
var i,j:integer;
begin
for i:=1 to n do
 begin
  for j:=1 to n do
  write(a[i,j]:7:3,' ');
  writeln;
 end;
end;
 
 
var a,b,obr:matr;
    i,j,n,k,z,p:integer;s:real;c:array[1..4,1..4] of real;
    pp:array[1..4,1..4] of string;
    rk:string;
 
 
begin
clrscr;
write('Vvedite N: ');
readln(n);
writeln('‚¢¥¤¨â¥ ',n*n,'elementov matricy:');
for i:=1 to n do
for j:=1 to n do
   begin
    write('a[',i,',',j,']=');
    readln(a[i,j]);
   end;
clrscr;
writeln('Ishodnaya matrica:');
print_matr(n,a);
ObrMatr(a,obr,n);
writeln('Obratnaya matrica:');
print_matr(n,obr);
readkey;
end.