matrix multiply

[jclemens]

This uses new array syntax:
'
'
' matrix multiply A*B giving C
' returns 0 on error, else 1
' the parameter symbolized by C should be passed by reference
Sub matmpy(A(),B(),C())
   dim adim(0)
    dim bdim(0)
    dim tmp(0)
   adim() = getdim(A())
   bdim() = getdim(B())
' must be 2 dims
  if adim(0)<>2 or bdim(0)<>2 then return 0
' number of columns of A must equal  number of rows of B
  if adim(2)<>bdim(1) then return 0
  for arow = 0 to adim(1)
    for bcol = 0 to bdim(2)
    '  A row vector multiplied pairwise by B column vector   
    tmp() = A(arow,*)*B(*,bcol)
      sum=0
      for k = 0 to adim(2)
      sum = sum  + tmp(k)
      next k
      C(arow,bcol) = sum
    next bcol
  next arow
  return 1
End Sub

[Chuck]

I think you could condense the inner loop:

     tmp() = A(arow,*)*B(*,bcol)
      sum=0
      for k = 0 to adim(2)
      sum = sum  + tmp(k)
      next k
      C(arow,bcol) = sum

to

     C(arow,bcol) = ArrSum(A(arow,*)*B(*,bcol))

It's wild how much easier it is to write this routine in Basic.

-Chuck

[jclemens]

That is neat‼ Extremely compact code and probably runs much faster. I didn't know about the existence of ArrSum, possibly because it doesn't appear in the list of array functions although it is in the index.  Here it is now:
'
' matrix multiply A*B giving C
' returns 0 on error, else 1
' the parameter symbolized by C should be passed by reference
Sub matmpy(A(),B(),C())
   dim adim(0)
    dim bdim(0)
   adim() = getdim(A())
   bdim() = getdim(B())
' must be 2 dims
  if adim(0)<>2 or bdim(0)<>2 then return 0
' number of columns of A must equal  number of rows of B
  if adim(2)<>bdim(1) then return 0
  for arow = 0 to adim(1)
    for bcol = 0 to bdim(2)
    '  A row vector multiplied pairwise by B column vector, then summed   
    C(arow,bcol) = ArrSum(A(arow,*)*B(*,bcol))
    next bcol
  next arow
  return 1
End Sub

[Chuck]

  dim adim(0)
    dim bdim(0)

These dims are no longer needed, those arrays will be initialized by the GetDim() function.

' must be 2 dims
  if adim(0)<>2 or bdim(0)<>2 then return 0
' number of columns of A must equal  number of rows of B
  if adim(2)<>bdim(1) then return 0

After you check the dimensions, you might as well Dim C()

dim C(adim(1), bdim(2))


That way the calling program doesn't have to dim C().

'
' matrix multiply A*B giving C
' returns 0 on error, else 1
' the parameter symbolized by C should be passed by reference
Sub matmpy(A(),B(),C())
  adim() = getdim(A())
  bdim() = getdim(B())
' must be 2 dims
  if adim(0)<>2 or bdim(0)<>2 then return 0
' number of columns of A must equal  number of rows of B
  if adim(2)<>bdim(1) then return 0

  dim C(adim(1), bdim(2))

  for arow = 0 to adim(1)
    for bcol = 0 to bdim(2)
    '  A row vector multiplied pairwise by B column vector, then summed  
    C(arow,bcol) = ArrSum(A(arow,*)*B(*,bcol))
    next bcol
  next arow
  return 1
End Sub


I have a java linear algebra library that has all the matrix functions. I will probably add built-in functions that use this library.

-Chuck