program secante			!!   25-May-2010
	implicit real*8 (a-h,o-z)

c....... by Dario Mitnik

c....... Finding the root of the function finput(x) by Secant Method 

	external finput,dfinput

	data rzero,one,two/0.0d0,1.0d0,2.0d0/
	
	
c....... files used:
c....... unit=20 --  secante.out (output)
	open(unit=20,file='secante.out',status='unknown')
	
c....... parameters for tolerance and convergence
	tolerance = 1.0d-6
	mxteps = 50
	
	print*,'give the interval for root finding (a and b)'
	read*,a
	print*,'a=:',a
	read*,b
	print*,'b=:',b
	print*,' '
	
	x1 = (a + b)/two
	x0 = x1 - x1/10.0d0
	
	do 100 i=1,mxteps
	
	    fx1 = finput(x1)
	    dfx1 = dfinput(x1,x0)
	    x2 = x1 - fx1/dfx1
	    dx = x2 - x1
	    write(20,555) x2,x1,dx,fx1
	    if (dabs(dx).le.tolerance) then
	                write(20,555) x2,finput(x2)
	    		print*,' root = ',x2,' in ',i,'  iterations'
			stop
	    endif
	    x0 = x1
	    x1 = x2	    
100	continue
555	format(3(1pg15.7,2x),1pg15.7)

	print*,' no convergence '

	stop
	end	
c	
c************************************************************************
c
	double precision function finput(x)
	implicit real*8 (a-h,o-z)
	
c....... input function

	finput = exp(x)*dlog(x) - x*x

	return
	end
c	
c************************************************************************
c
	double precision function dfinput(x1,x0)
	implicit real*8 (a-h,o-z)
	
c....... derivative of input function

	data one,two/1.0d0,2.0d0/
	
	dfinput = (finput(x1)-finput(x0))/(x1-x0)

	return
	end
c	
c************************************************************************
c