subroutine fdjac2(fcn,m,n,x,fvec,fjac,ldfjac,iflag,epsfcn,wa) integer m,n,ldfjac,iflag double precision epsfcn double precision x(n),fvec(m),fjac(ldfjac,n),wa(m) c ********** c c subroutine fdjac2 c c this subroutine computes a forward-difference approximation c to the m by n jacobian matrix associated with a specified c problem of m functions in n variables. c c the subroutine statement is c c subroutine fdjac2(fcn,m,n,x,fvec,fjac,ldfjac,iflag,epsfcn,wa) c c where c c fcn is the name of the user-supplied subroutine which c calculates the functions. fcn must be declared c in an external statement in the user calling c program, and should be written as follows. c c subroutine fcn(m,n,x,fvec,iflag) c integer m,n,iflag c double precision x(n),fvec(m) c ---------- c calculate the functions at x and c return this vector in fvec. c ---------- c return c end c c the value of iflag should not be changed by fcn unless c the user wants to terminate execution of fdjac2. c in this case set iflag to a negative integer. c c m is a positive integer input variable set to the number c of functions. c c n is a positive integer input variable set to the number c of variables. n must not exceed m. c c x is an input array of length n. c c fvec is an input array of length m which must contain the c functions evaluated at x. c c fjac is an output m by n array which contains the c approximation to the jacobian matrix evaluated at x. c c ldfjac is a positive integer input variable not less than m c which specifies the leading dimension of the array fjac. c c iflag is an integer variable which can be used to terminate c the execution of fdjac2. see description of fcn. c c epsfcn is an input variable used in determining a suitable c step length for the forward-difference approximation. this c approximation assumes that the relative errors in the c functions are of the order of epsfcn. if epsfcn is less c than the machine precision, it is assumed that the relative c errors in the functions are of the order of the machine c precision. c c wa is a work array of length m. c c subprograms called c c user-supplied ...... fcn c c minpack-supplied ... dpmpar c c fortran-supplied ... dabs,dmax1,dsqrt c c argonne national laboratory. minpack project. march 1980. c burton s. garbow, kenneth e. hillstrom, jorge j. more c c ********** integer i,j double precision eps,epsmch,h,temp,zero double precision dpmpar data zero /0.0d0/ c c epsmch is the machine precision. c epsmch = dpmpar(1) c eps = dsqrt(dmax1(epsfcn,epsmch)) do 20 j = 1, n temp = x(j) h = eps*dabs(temp) if (h .eq. zero) h = eps x(j) = temp + h call fcn(m,n,x,wa,iflag) if (iflag .lt. 0) go to 30 x(j) = temp do 10 i = 1, m fjac(i,j) = (wa(i) - fvec(i))/h 10 continue 20 continue 30 continue return c c last card of subroutine fdjac2. c end