share/hompack/fortran/multds.f

   1       SUBROUTINE MULTDS(Y,AA,X,MAXA,NN,LENAA)
   2 C
   3 C     This subroutine accepts a matrix, AA, in packed skyline storage form and
   4 C       a vector, x, and returns the product AA*x in y.
   5 C
   6 C     Input Variables:
   7 C
   8 C       AA -- one dimensional real array containing the NN x NN matrix in
   9 C             packed skyline storage form.
  10 C
  11 C       x -- real vector of length NN to be multiplied by AA.
  12 C
  13 C       MAXA -- integer array used for specifying information about AA.
  14 C               MAXA has length NN+1, and stores the indices of the
  15 C               diagonal elements of the matrix packed in AA.  By
  16 C               convention, MAXA(NN+1) = LENAA + 1 .
  17 C
  18 C       NN -- dimension of the matrix packed in AA .
  19 C
  20 C       LENAA -- number of elements in AA.
  21 C
  22 C
  23 C     Output Variables:
  24 C
  25 C       y -- real vector of length NN containing the product  AA*x .
  26 C
  27 C
  28 C
  29       INTEGER I,II,KK,KL,KU,LENAA,NN,MAXA(NN+1)
  30       DOUBLE PRECISION AA(LENAA),B,CC,X(NN),Y(NN)
  31       IF(LENAA.GT.NN) GO TO 20
  32       DO 10 I=1,NN
  33    10 Y(I)=AA(I)*X(I)
  34       RETURN
  35    20 DO 40 I=1,NN
  36    40 Y(I)=0.00
  37       DO 100 I=1,NN
  38       KL=MAXA(I)
  39       KU=MAXA(I+1)-1
  40       II=I+1
  41       CC=X(I)
  42       DO 100 KK=KL,KU
  43       II=II-1
  44   100 Y(II)=Y(II)+AA(KK)*CC
  45       IF(NN.EQ.1) RETURN
  46       DO 200 I=2,NN
  47       KL=MAXA(I)+1
  48       KU=MAXA(I+1)-1
  49       IF(KU-KL) 200,210,210
  50   210 II=I
  51       B=0.00
  52       DO 220 KK=KL,KU
  53       II=II-1
  54   220 B=B+AA(KK)*X(II)
  55       Y(I)=Y(I)+B
  56   200 CONTINUE
  57       RETURN
  58       END