      SUBROUTINE SPOFA(A,LDA,N,INFO)
      INTEGER LDA,N,INFO
      REAL A(LDA,1)
C
C     SPOFA FACTORS A REAL SYMMETRIC POSITIVE DEFINITE
C     MATRIX.
C
C     SPOFA IS USUALLY CALLED BY SPOCO, BUT IT CAN BE CALLED
C     DIRECTLY WITH A SAVING IN TIME IF  RCOND  IS NOT NEEDED.
C     (TIME FOR SPOCO) = (1 + 18/N)*(TIME FOR SPOFA) .
C
C     ON ENTRY
C
C        A       REAL(LDA, N)
C                THE SYMMETRIC MATRIX TO BE FACTORED.  ONLY THE
C                DIAGONAL AND UPPER TRIANGLE ARE USED.
C
C        LDA     INTEGER
C                THE LEADING DIMENSION OF THE ARRAY  A .
C
C        N       INTEGER
C                THE ORDER OF THE MATRIX  A .
C
C     ON RETURN
C
C        A       AN UPPER TRIANGULAR MATRIX  R  SO THAT  A = TRANS(R)*R
C                WHERE  TRANS(R)  IS THE TRANSPOSE.
C                THE STRICT LOWER TRIANGLE IS UNALTERED.
C                IF  INFO .NE. 0 , THE FACTORIZATION IS NOT COMPLETE.
C
C        INFO    INTEGER
C                = 0  FOR NORMAL RETURN.
C                = K  SIGNALS AN ERROR CONDITION.  THE LEADING MINOR
C                     OF ORDER  K  IS NOT POSITIVE DEFINITE.
C
C     LINPACK.  THIS VERSION DATED 08/14/78 .
C     CLEVE MOLER, UNIVERSITY OF NEW MEXICO, ARGONNE NATIONAL LAB.
C
C     SUBROUTINES AND FUNCTIONS
C
C     BLAS SDOT
C     FORTRAN SQRT
C
C     INTERNAL VARIABLES
C
      REAL SDOT,T
      REAL S
      INTEGER J,JM1,K
C     BEGIN BLOCK WITH ...EXITS TO 40
C
C
         DO 30 J = 1, N
            INFO = J
            S = 0.0E0
            JM1 = J - 1
            IF (JM1 .LT. 1) GO TO 20
            DO 10 K = 1, JM1
               T = A(K,J) - SDOT(K-1,A(1,K),1,A(1,J),1)
               T = T/A(K,K)
               A(K,J) = T
               S = S + T*T
   10       CONTINUE
   20       CONTINUE
            S = A(J,J) - S
C     ......EXIT
            IF (S .LE. 0.0E0) GO TO 40
            A(J,J) = SQRT(S)
   30    CONTINUE
         INFO = 0
   40 CONTINUE
      RETURN
      END
