share/hompack/fortran/mulp.f

   1       SUBROUTINE MULP(XXXX,YYYY,ZZZZ)
   2 C
   3 C THIS SUBROUTINE PERFORMS MULTIPLICATION OF COMPLEX NUMBERS:
   4 C ZZZZ = XXXX*YYYY
   5 C
   6 C NOTE:  IN THE CALLING ROUTINE, ZZZZ SHOULD NOT BE THE SAME
   7 C AS XXXX OR YYYY.  HOWEVER, XXXX MAY BE THE SAME AS YYYY.
   8 C THUS, "CALL MULP(X,X,Z)" IS OK, BUT "CALL MULP(X,Y,X)" IS NOT.
   9 C
  10 C ON INPUT:
  11 C
  12 C XXXX  IS AN ARRAY OF LENGTH TWO REPRESENTING THE FIRST COMPLEX
  13 C       NUMBER, WHERE XXXX(1) = REAL PART OF XXXX AND XXXX(2) =
  14 C       IMAGINARY PART OF XXXX.
  15 C
  16 C YYYY  IS AN ARRAY OF LENGTH TWO REPRESENTING THE SECOND COMPLEX
  17 C       NUMBER, WHERE YYYY(1) = REAL PART OF YYYY AND YYYY(2) =
  18 C       IMAGINARY PART OF YYYY.
  19 C
  20 C ON OUTPUT:
  21 C
  22 C ZZZZ  IS AN ARRAY OF LENGTH TWO REPRESENTING THE RESULT OF
  23 C       THE MULTIPLICATION, ZZZZ = XXXX*YYYY, WHERE ZZZZ(1) =
  24 C       REAL PART OF ZZZZ AND ZZZZ(2) = IMAGINARY PART OF ZZZZ.
  25 C
  26 C DECLARATION OF INPUT
  27       DOUBLE PRECISION XXXX,YYYY
  28       DIMENSION XXXX(2),YYYY(2)
  29 C
  30 C DECLARATION OF OUTPUT
  31       DOUBLE PRECISION ZZZZ
  32       DIMENSION ZZZZ(2)
  33 C
  34       ZZZZ(1) = XXXX(1)*YYYY(1) - XXXX(2)*YYYY(2)
  35       ZZZZ(2) = XXXX(1)*YYYY(2) + XXXX(2)*YYYY(1)
  36       RETURN
  37       END