with function getInterestRate (pv in number, fv in number, pmt in number, nper in number, type in number )
    return number is rate number;
begin
	declare
		guess number(6,3) := .1;
		rate binary_double;
		financial_max_iterations number(10) := 100;
		financial_precision binary_double := .000001;
		y binary_double;
		y0 binary_double;
		y1 binary_double;
		f binary_double;
		i number(10);
		x0 binary_double := 0;
		x1 binary_double;
begin
	rate := guess;
if(abs(rate) < financial_precision) then y := pv * (1 + nper * rate) + pmt * (1 + rate * type) * nper + fv;
									else
										f := exp(nper * ln(1 + rate));
										y := pv * f + pmt * (1 / rate + type) * (f - 1) + fv;
									end if;

y0 := pv + pmt * nper + fv;
y1 := pv * f + pmt * (1 / rate + type) * (f - 1) + fv;

i  := x0 ;
x1 := rate;

while ((abs(y0 - y1) > financial_precision) and (i < financial_max_iterations)) 
loop
    rate := (y1 * x0 - y0 * x1) / (y1 - y0);
    x0 := x1;
    x1 := rate;

    if (abs(rate) < financial_precision) then 	y := pv * (1 + nper * rate) + pmt * (1 + rate * type) * nper + fv;
										 else 
												f := exp(nper * ln(1 + rate));
												y := pv * f + pmt * (1 / rate + type) * (f - 1) + fv;
										 end if;

    y0 := y1;
    y1 := y;
    i := i + 1;
end loop;
return rate;
end;
end;
/* select getInterestRate(15000, 0, -2000, 6, 0) as p from dual */
/* select getInterestRate(2531, 0, -749, 36, 0) as p from dual */

CREATE OR REPLACE FUNCTION fnc_g_div_gp(r in number, n in number, p in number, x in number, y in number, w in number)
    return number                    
    is

   /* Evaluate g(r_n)/g'(r_n), where g := fv + pv*(1+rate)**nper + pmt*(1+rate*when)/rate * ((1+rate)**nper - 1)*/
   
     t1  number;
     t2  number;
     g  number;
     gp  number;
     res  number;
 
   begin
     

    t1 := power((r+1),n);
    t2 := power((r+1),(n-1));
    g := y + t1 * x + p * (t1 - 1) * (r * w + 1) / r;
    gp := (n * t2 * x - p * (t1 - 1) * (r * w + 1) / (power(r,2)) + n * p * t2 * (r * w + 1) / r + p * (t1 - 1) * w/ r);
    res := g / gp;
 
   return res;
     
  end;

with function fnc_getRate(nper in number, pmt in number, pv in number, fv in number, type_ in number)
    return number                  
    is

   /* Evaluate g(r_n)/g'(r_n), where g := fv + pv*(1+rate)**nper + pmt*(1+rate*when)/rate * ((1+rate)**nper - 1)*/
 begin
    declare
        guess number(6,3) := .5;
        rate number;
        maxiter number(10) := 100;
        tol number := .000001;
        close_ number := 0;
        
        iterator  number;
        rn  number;
        rnp1  number;
        diff  number;
        g  number;
 
   begin
     
    rn := guess;
 	iterator := 0;
 	while (iterator < maxiter)
        loop
            rnp1 := rn - fnc_g_div_gp(rn, nper, pmt, pv, fv, type_);
            diff := abs(rnp1 - rn);
            iterator := iterator + 1;
            rn := rnp1;
        end loop;
 	return rn;
   end;
end;

select fnc_getRate(36,749,-2531,0,0) as rate from dual
;