PROGRAM D10r4

! Driver for routine dbrent

! The function dbrent has been converted to a subroutine.

LIBRARY "dbrent", "mnbrak", "bessj0"
DECLARE FUNCTION bessj0
DECLARE FUNCTION func, df         ! Defined below

DIM amin(20)

CLEAR
LET tol = .000001
LET eql = .0001
LET nmin = 0

PRINT "Minima of the function bessj0"
PRINT
PRINT "    min. #       x       bessj0(x)   bessj1(x)     dbrent"
PRINT
FOR i = 1 to 100
    LET ax = i
    LET bx = i + 1

    CALL mnbrak (ax, bx, cx, fa, fb, fc, dum)
    CALL dbrent (ax, bx, cx, dum, deriv, tol, dbr, xmin)

    IF nmin = 0 then
       LET amin(1) = xmin
       LET nmin = 1
       PRINT using "#######": nmin;
       PRINT "   ";
       PRINT using "----#.######": xmin, bessj0(xmin), df(xmin), dbr
    ELSE
       LET iflag = 0
       FOR j = 1 to nmin
           IF abs(xmin - amin(j)) <= eql * xmin then LET iflag = 1
       NEXT j
       IF iflag = 0 then
          LET nmin = nmin + 1
          LET amin(nmin) = xmin
          PRINT using "#######": nmin;
          PRINT "   ";
          PRINT using "----#.######": xmin, bessj0(xmin), df(xmin), dbr
       END IF
    END IF
NEXT i

END

FUNCTION df (x)
    LIBRARY "bessj1"
    DECLARE FUNCTION bessj1
    LET df = -bessj1(x)
END FUNCTION

FUNCTION func (x)
    LIBRARY "bessj0"
    DECLARE FUNCTION bessj0
    LET func = bessj0(x)
END FUNCTION