How to exchange rows in a matrix

Problem/Question/Abstract:

I'm working with a matrix and I've chosen to use an Array of Array of real to do it (Is it the best way? I need the elements to be of real type). The problem is that I must change a certain line with another. For example, change the first line of the matrix with the second one. How do I do it quickly? I don't want to move element by element.

Answer:

program Matrices;

{$APPTYPE CONSOLE}

uses
  SysUtils;

type
  TMatrixRow = array of Double; {preferrable to Real}
  TMatrix = array of TMatrixRow;

procedure MatrixExchangeRows(M: TMatrix; First, Second: Integer);
var
  Help: TMatrixRow;
begin
  if (First < 0) or (First > High(M)) or (Second < 0) or (Second > High(M)) then
    Exit; {or whatever you like.}
  {Only pointers are exchanged!}
  Help := M[First];
  M[First] := M[Second];
  M[Second] := Help;
end;

procedure MatrixWrite(M: TMatrix);
var
  Row, Col: Integer;
begin
  for Row := 0 to High(M) do
  begin
    for Col := 0 to High(M[Row]) do
      Write(M[Row, Col]: 10: 2);
    Writeln;
  end;
  Writeln;
end;

var
  Matrix: TMatrix;
  Row, Column: Integer;

begin
  Randomize;
  SetLength(Matrix, 4, 4);
  for Row := 0 to High(Matrix) do
    for Column := 0 to High(Matrix[Row]) do
      Matrix[Row, Column] := Random * 1000.0;
  MatrixWrite(Matrix);
  MatrixExchangeRows(Matrix, 1, 2);
  MatrixWrite(Matrix);
  Readln;
end.