' -----------------------------------
' MAIN RECURSIVE FUNCTION -----------
' THAT ACTUALLY DOES ALL WORK -------
' -----------------------------------

function determinant(array, size as integer) as floating

  if size < 2 then
    Print "Cannot determine determinant!";
    while not readkey wend
    Stop

  elseif size = 2 then
    return array[1,1]*array[2,2] - array[2,1]*array[1,2]

  else

    sum = 0

    for j=1 to size

      ' Skip zero factors to speed up

      if (array[1,j] <> 0) then

        Dim new_a(size,size)

        ' Creating new matrix
        for c1=2 to size
          for c2=1 to size
            if c2 > j then 
               new_a[c1-1,c2-1] =array[c1,c2] 
            elseif c2 < j then 
               new_a[c1-1,c2]= array[c1,c2]
            endif
          Next
        Next

        ' Recursive call to get the determinant of smaller matrix.

        factor = array[1,j]*determinant(new_a, size-1)

        ' The alternating law applies here

        if (j mod 2 = 0) then 
           sum = sum - factor
        else 
           sum = sum + factor
        endif

      endif

    Next

    return sum

  endif

end function

'--------------------------------------------------------------------
' ------------------------------------------------------------------
'--------------------------------------------------------------------

ConsoleTextColor Rgb(0,0,100)
print " Matrix determinant calculation" : print

ConsoleTextColor Rgb(0,0,0)
Dim size as Integer
input " Enter matrix size: ", size

Dim Matrix(size,size) 'declare 2 dimension array

' Let's input matrix ------------------------
cls
ConsoleTextColor Rgb(0,100,0)

for x=1 to size
  for y=1 to size
    print " input Matrix[",x,",",y,"]"
    input " >", Matrix[x,y]
  next
next

' let's print matrix -----------------
cls
Print " Your matrix: "
ConsoleTextColor Rgb(0,100,0)


for x=1 to size

  dim str as string

  for y=1 to size
    str = str + Matrix[x,y] + "   "
  next

  print " ",str

next

' Determinant calculation ------------
 Dim Det as floating
 Det = determinant(Matrix, size)
' ------------------------------------

ConsoleTextColor Rgb(125,125,125)
print : print " Determinant = ", Det
ConsoleTextColor 0

InfoBox "Press any key to exit"
while not readkey wend