Проверка в методе ньютона

program lab_5;
uses crt;
type matrix=array[1..4,1..4] of real;
     vector=array[1..4] of real;
var a,b:matrix;
 
  procedure obr(var a,b:matrix);
    var i,j,k:integer; c:real;
  begin
    for i:=1 to 4 do
      for j:=1 to 4 do
        if i=j then b[i,j]:=1 else b[i,j]:=0;
    for k:=1 to 3 do begin
      if a[k,k]=0 then
        for i:=k+1 to 3 do
          if a[i,k]<>0 then begin
            for j:=1 to 4  do begin c:=a[k,j]; a[k,j]:=a[i,j]; a[i,j]:=c; end;
            for j:=1 to 4  do begin c:=b[k,j]; b[k,j]:=b[i,j]; b[i,j]:=c; end;
            break;
          end;
 
      for i:=k+1 to 4 do begin
        c:=-a[i,k]/a[k,k];
        for j:=1 to 4 do a[i,j]:=a[i,j]+c*a[k,j];
        for j:=1 to 4 do b[i,j]:=b[i,j]+c*b[k,j];
      end;
    end;
    for k:=4 downto 2 do
      for i:=k-1 downto 1 do begin
        c:=-a[i,k]/a[k,k];
        for j:=1 to 4 do a[i,j]:=a[i,j]+c*a[k,j];
        for j:=1 to 4 do b[i,j]:=b[i,j]+c*b[k,j];
      end;
    for i:=1 to 4 do begin
      c:=a[i,i];
      for j:=1 to 4 do a[i,j]:=a[i,j]/c;
      for j:=1 to 4 do b[i,j]:=b[i,j]/c;
    end;
  end;
 
  procedure gen(var a:matrix);
    var i,j:integer;
  begin
    for i:=1 to 4 do begin
      for j:=1 to 4 do a[i,j]:=random(10);
    end;
  end;
 
 procedure show(var a:matrix);
    var i,j:integer;
  begin
    for i:=1 to 2 do begin
      for j:=1 to 2 do write(a[i,j]:7:3);
     writeln
    end;
    writeln;
  end;
 
begin
clrscr; gen(a); show(a); obr(a,b); show(a); show(b); readkey;
 
end.