DEFINITION MODULE BSStepM;

   (* EXPORT QUALIFIED RZExtr, PZExtr, BSStep; *)

   FROM NRMath IMPORT DerivFunction;
   FROM NRVect IMPORT Vector;

   PROCEDURE RZExtr(iest: INTEGER; 
                    xest: REAL; 
                    YEST, YZ, DY: Vector; 
                    nuse: INTEGER); 
   (*
     Use diagonal rational function extrapolation to evaluate 
     n functions at x=0 by fitting a diagonal rational
     function to a sequence of estimates with progressively smaller 
     values x=xest, and corresponding function vectors YEST[0, n-1].
     This call is number iest in the sequence of calls.
     The extrapolation uses at most the last nuse estimates. 
     Extrapolated function values are output as YZ[0, n-1], and their
     estimated error is output as DY[0, n-1].
   *)

   PROCEDURE PZExtr(iest: INTEGER; 
                    xest: REAL; 
                    YEST, YZ, DY: Vector; 
                    nuse: INTEGER); 

   PROCEDURE BSStep(    Y, DYDX:     Vector; 
                    VAR x:           REAL; 
                        htry, eps:   REAL; 
                        YSCAL:       Vector; 
                        derivs:      DerivFunction;
                    VAR hdid, hnext: REAL); 
   (*
     Bulirsch-Stoer step with monitoring of local
     truncation error to ensure accuracy and to adjust the stepsize.
     Input are the dependent variable vector Y[0, n-1] and its derivative
     DYDX[0, n-1] at the starting value of the independent variable x.  
     Also input are the stepsize to be attempted htry, the required 
     accuracy eps, and the vector YSCAL[0, n-1] against which the error 
     is scaled. On output, Y and x are replaced by their new values, hdid
     is the stepsize which was actually accomplished, and hnext is
     the estimated next stepsize.  derivs is the user-supplied routine
     that computes the right-hand side derivatives.
   *)

END BSStepM.