[非线性] hybrd算法求解非线性方程组

subroutine function_equations(n,x,fvec,iflag)
 implicit none
 integer n,iflag
 double precision x(n),fvec(n)
! ------------------------------------------------
 fvec(1) = 3d0*x(1)-cos(x(2)*x(3))-0.5d0
 fvec(2) = x(1)**2-81d0*(x(2)+0.1d0)**2+sin(x(3))+1.06d0
 fvec(3) = dexp(-x(1)*x(2))+20d0*x(3)+(10d0*3.1415926d0-3d0)/3d0
 return
 end 
 program main_test
 implicit none
 external function_equations
 integer,parameter :: n=3 ,lwa=(n*(3*n+13))/2 
 double precision x(n),fvec(n)
 double precision,parameter :: tol = 1d-8
 double precision wa(lwa)
 integer info

 wa(lwa) = 1d0

! hybrd1(fcn,n,x,fvec,tol,info,wa,lwa)
 call hybrd1(function_equations,n,x,fvec,tol,info,wa,lwa)
 end