subroutine gauss(RO,AP,MT,M,N,*)
c
c CALCULATES (RO**(-1))*AP BY GAUSS ELIMINATION
c RO IS A SQUARE MATRIX
c THE CALCULATED PRODUCT IS STORED IN AP
c ABNORMAL EXIT IF RO IS SINGULAR
c       
      integer MT, M, N, M1,I,J,IM,
     & I1,MI,MI1    
      double precision RO(MT,M),AP(MT,N),X,RM,PR,
     &  Y  
      if(M.ne.1)goto 10
      X=RO(1,1)
      if(dabs(X).le.1.0D-13) return 1
      X=1.0/X
      do 16 I=1,N
16     AP(1,I)=AP(1,I)*X
       return
10     continue
        M1=M-1
        DO1 I=1,M1
        IM=I
        RM=DABS(RO(I,I))
        I1=I+1
        do 2 J=I1,M
        if(DABS(RO(J,I)).LE.RM) goto 2
        RM=DABS(RO(J,I))
        IM=J
2       continue
        If(IM.eq.I)goto 17
        do 3 J=1,N
        PR=AP(I,J)
        AP(I,J)=AP(IM,J)
3       AP(IM,J)=PR
        do 4 J=I,M
        PR=RO(I,J)
        RO(I,J)=RO(IM,J)
4       RO(IM,J)=PR
17      X=RO(I,I)
        if(dabs(X).le.1.0E-13) return 1
        X=1.0/X
        do 5 J=1,N
5       AP(I,J)=X*AP(I,J)
        do 6 J=I1,M
6       RO(I,J)=X*RO(I,J)
        do 7 J=I1,M
        Y=RO(J,I)
        do 8 K=1,N
8       AP(J,K)=AP(J,K)-Y*AP(I,K)
        do 9 K=I1,M
9       RO(J,K)=RO(J,K)-Y*RO(I,K)
7       continue
1       continue
        X=RO(M,M)
        if(dabs(X).le.1.0E-13) return 1
        X=1.0/X
        do 11 J=1,N
11      AP(M,J)=X*AP(M,J)
        do 12 I=1,M1
        MI=M-I
        MI1=MI+1
        do 14 J=1,N
        X=AP(MI,J)
        do 15 K=MI1,M
15      X=X-AP(K,J)*RO(MI,K)
14      AP(MI,J)=X
12      continue
        return
        end